Turn the Files tab into a real file manager

Rename, an in-app viewer for text and images, host-to-container drag and
drop, New folder, keyboard operation — plus the pre-existing bugs the new
surface would otherwise have been built on top of.

New Tauri commands (file_commands.rs, registered in lib.rs):

* rename_container_path — `mv -n -- <from> <parent>/<name>` through
  exec_oneshot_as, so the *exit code* is checked. exec_oneshot discards the
  status and interleaves stderr into stdout, which would have made a
  permission failure look like a success. `mv -n` on its own is not enough
  either: GNU coreutils makes its refusal to clobber silent and exits 0, so
  an explicit `test -e` on the destination is what turns a name clash into
  an error the user sees. `mv`'s own words are surfaced, since renames
  outside /workspace legitimately fail on permissions. The new name is
  validated in Rust (no `/`, no NUL, not "." / ".." / empty, ≤255 bytes) —
  it is user text going into argv, and a name with a separator would be a
  move rather than a rename.
* read_container_file — exact bytes via Docker's archive endpoint, returned
  as base64. Deliberately not exec_oneshot, which runs every chunk through
  String::from_utf8_lossy and merges stderr, so it would corrupt any
  non-UTF-8 file and could splice diagnostics into content. Base64 rather
  than Vec<u8> because Tauri serialises a byte vec as a JSON number array.
  Capped and truncation-reporting; the caller picks the cap (images get 5
  MiB against text's 1 MiB, being the kind that blows a text-sized budget)
  and Rust clamps it to 8 MiB regardless.
* create_container_directory — `mkdir` without -p, so a clash is an error
  rather than a silent success. Named for its siblings rather than the bare
  `create_directory` in the brief.

The tar-extraction half of download_container_file is now the shared
fetch_container_file() both commands use, and it abandons the transfer once
a capped read has what it needs.

Frontend:

* Single click selects, double click opens. Directory navigation moved onto
  double click too — a single click used to navigate, which made it
  impossible to select a directory in order to rename it. Rows are now
  focusable and the table is a real `grid`: Enter opens, F2 renames, arrows
  walk the rows. No outline suppression; the global :focus-visible ring is
  what shows focus.
* FileViewerModal (built on ui/Modal, the only correct dialog) renders text
  in a <pre> and images from a revocable blob: URL. tauri.conf.json's
  img-src had neither `data:` nor `blob:`, so an in-app image was blocked by
  CSP; `blob:` is added — revocable, and no megabytes of base64 in the DOM.
  The asset protocol stays disabled. Anything else gets a "Save to host"
  state instead of a broken preview, decided by extension and then by
  sniffing the bytes for NUL.
* Host drag-and-drop uses Tauri's native onDragDropEvent, mirroring
  TerminalView: HTML5 ondrop carries no paths and is blocked in the webview
  on Windows by dragDropEnabled, which the terminal needs. The listener is
  window-wide, so it routes by hit-testing the payload position (physical
  pixels, hence the devicePixelRatio divide) against the pane's rect — a
  hidden pane has a zero-size rect and never matches, which is what keeps
  this and the terminal's listener apart. enter/over/leave drive a drop
  highlight.
* Per-row Download is now "Save to host…"; directories no longer offer it.

Pre-existing bugs fixed:

* Uploaded files landed root:root with a 1970 mtime. tar::Header::new_gnu()
  zeroes uid/gid/mtime and Docker honours the header verbatim, so uploads
  were not writable by `claude`. All four single-file tar builds now go
  through build_single_file_tar() with the container user's ids, read from
  the container because entrypoint.sh remaps them to the host user on Unix
  and deliberately does not on Windows.
* Symlinked directories could not be opened: `find -printf '%y'` reports `l`.
  The listing now prints `%Y` as well, so is_directory dereferences and a
  new is_symlink carries what `%y` used to say. The row labels the link.
* upload_file_to_container had no size cap and did a synchronous fs::read on
  an async worker. Now 256 MiB (matching the terminal drop path) with the
  read and tar build in spawn_blocking, and the host mtime preserved.
* A directory passed to upload reached fs::read and produced an opaque "Is a
  directory". Rejected with an explanation instead — recursive upload is a
  larger feature than this panel needs.
* download_container_file wrote the *first tar entry*, so downloading a
  directory silently produced a garbage file. Non-regular entries are now an
  explicit error.

Tests: 46 new (33 frontend across FilesTab, useFileManager and filePreview;
12 Rust covering the find-output parser and the rename validator, neither of
which had any). 405 frontend / 297 Rust, both green.

No drag-out dependency was added — tauri-plugin-drag is not introduced and
OS drag-out is not attempted; that stays deferred, with "Save to host…" as
the way files leave the container.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GBq2rGum6GX7xXgsas1fDc

app/src/components/projects/home/filePreview.ts

@@ -0,0 +1,107 @@
+/**
+ * What the Files viewer can show, and how much of it to ask for.
+ *
+ * Pure helpers, deliberately separate from the modal: the type sniffing is
+ * where a preview quietly turns into a screenful of mojibake, and it is worth
+ * testing without a container.
+ */
+
+/**
+ * Extension → MIME, for the raster/vector types an `<img>` actually renders.
+ * The MIME matters because the bytes are handed to the DOM as a `Blob`, and a
+ * blob with the wrong (or empty) type will not decode.
+ */
+const IMAGE_MIME: Record<string, string> = {
+  png: "image/png",
+  jpg: "image/jpeg",
+  jpeg: "image/jpeg",
+  gif: "image/gif",
+  webp: "image/webp",
+  bmp: "image/bmp",
+  ico: "image/x-icon",
+  avif: "image/avif",
+  // Safe in an `<img>`: that context cannot run the script an SVG may carry.
+  svg: "image/svg+xml",
+};
+
+/** Extensions we are confident are text, so no byte sniffing is needed. */
+const TEXT_EXTENSIONS = new Set([
+  "txt", "md", "markdown", "rst", "log", "csv", "tsv",
+  "json", "jsonc", "yaml", "yml", "toml", "ini", "cfg", "conf", "env", "properties",
+  "js", "jsx", "mjs", "cjs", "ts", "tsx", "rs", "py", "rb", "go", "java", "kt",
+  "c", "h", "cc", "cpp", "hpp", "cs", "php", "swift", "scala", "lua", "pl", "r",
+  "sh", "bash", "zsh", "fish", "ps1", "bat",
+  "html", "htm", "xml", "svelte", "vue", "css", "scss", "sass", "less",
+  "sql", "graphql", "gql", "proto", "diff", "patch", "lock", "gitignore",
+  "dockerfile", "makefile", "cmake", "gradle", "tf", "tfvars",
+]);
+
+/** Extensionless files that are text by convention. */
+const TEXT_BASENAMES = new Set([
+  "dockerfile", "makefile", "readme", "license", "licence", "changelog",
+  "authors", "notice", "copying", "procfile", "rakefile", "gemfile", "vagrantfile",
+  // Dotfiles: the leading dot is stripped before the lookup.
+  "gitignore", "gitattributes", "gitmodules", "dockerignore", "npmrc", "nvmrc",
+  "editorconfig", "bashrc", "zshrc", "profile", "env",
+]);
+
+/** 1 MiB of text is already far more than anyone reads in a modal. */
+export const TEXT_PREVIEW_LIMIT = 1024 * 1024;
+/**
+ * Images get five times the budget: they are the file kind that routinely
+ * blows past a text-sized cap, and a half-read image is not a preview at all —
+ * it either decodes whole or it does not.
+ */
+export const IMAGE_PREVIEW_LIMIT = 5 * 1024 * 1024;
+
+/** Lowercased extension, or "" for an extensionless name. */
+export function extensionOf(name: string): string {
+  const base = name.slice(name.lastIndexOf("/") + 1);
+  const dot = base.lastIndexOf(".");
+  // A leading dot is "hidden file", not "extension" (`.gitignore`).
+  if (dot <= 0) return "";
+  return base.slice(dot + 1).toLowerCase();
+}
+
+/** The MIME to build the Blob with, or null if this is not a previewable image. */
+export function imageMimeFor(name: string): string | null {
+  return IMAGE_MIME[extensionOf(name)] ?? null;
+}
+
+export type PreviewKind = "image" | "text" | "unknown";
+
+/**
+ * A first guess from the name alone. `unknown` is not a refusal — the viewer
+ * reads the bytes and falls back to sniffing them, so a `.bak` of a config
+ * file still previews.
+ */
+export function previewKind(name: string): PreviewKind {
+  if (imageMimeFor(name)) return "image";
+  const ext = extensionOf(name);
+  if (ext) return TEXT_EXTENSIONS.has(ext) ? "text" : "unknown";
+  const base = name.slice(name.lastIndexOf("/") + 1).replace(/^\./, "").toLowerCase();
+  return TEXT_BASENAMES.has(base) ? "text" : "unknown";
+}
+
+/** How many bytes to ask the backend for, given what we expect to render. */
+export function previewLimit(name: string): number {
+  return previewKind(name) === "image" ? IMAGE_PREVIEW_LIMIT : TEXT_PREVIEW_LIMIT;
+}
+
+/** Base64 → bytes. `atob` yields a binary string; widen it one char at a time. */
+export function decodeBase64(base64: string): Uint8Array<ArrayBuffer> {
+  const binary = atob(base64);
+  const bytes = new Uint8Array(new ArrayBuffer(binary.length));
+  for (let i = 0; i < binary.length; i++) bytes[i] = binary.charCodeAt(i);
+  return bytes;
+}
+
+/**
+ * The classic heuristic: a NUL byte early on means this is not text. Cheap,
+ * and it is what `git` and `grep` use to decide the same question.
+ */
+export function looksBinary(bytes: Uint8Array): boolean {
+  const limit = Math.min(bytes.length, 8000);
+  for (let i = 0; i < limit; i++) if (bytes[i] === 0) return true;
+  return false;
+}