Hold back the Disk panel and OS drag-out from the ship branch

This is a scope reduction, not an abandonment. Both subsystems are
preserved in full on `hold/disk-and-dragout` and are intended to come
back once they have been hardened separately. Nothing here is a
judgement that the features are unwanted — three successive
audit-and-fix cycles each closed a critical defect in these two areas
and each opened a new one, so the rest of the round ships now and these
two get their own cycle rather than holding it up.

Removed: the Disk settings panel and its whole reclaim / destroy /
compaction surface — `DiskSettings`, `DiskProjectTable`, `useDiskUsage`,
`docker/disk.rs`, `disk_tests.rs`, the disk commands in
`docker_commands.rs`, and their `generate_handler!` entries. Dropping
the IPC entries is the point: a UI-only removal would have left five
commands callable by a compromised webview, one of them a verified
arbitrary-DELETE primitive. `sweep_orphaned_snapshots`'s *command* goes
with them (the panel was its only caller); the sweep itself stays.

Removed: OS drag-out from the Files tab — `stage_container_file_for_drag`
and its host staging lifecycle, the pointer gesture and `dragPreview`,
`stageForDrag` / `isStagedHostPath`, the `tauri-plugin-drag` and
`@crabnebula/tauri-plugin-drag` dependencies, and the
`drag:allow-start-drag` capability grant, which could not be scoped.
The capability test's expected list is updated; its `*:default` and
`store:*` assertions are untouched.

Kept, deliberately: drag-and-drop *into* the app (Files pane and
terminal) and "Save to host…", which is now the only route out of a
container. The prevention work is untouched — the pre-commit scrub and
`SNAPSHOT_SCRUB_PATHS`, capped container logs, the `triple-c.base` /
`triple-c.managed` labels, `sweep_orphaned_snapshots` and the startup
housekeeping, the migration pin/probe reapers, scheduler log pruning,
`formatBytes.ts`, and `project_lock.rs` in full with every acquisition
site outside `disk.rs`.

Entanglements, resolved rather than deleted blind:
* `container.rs`'s `a_compaction_runs_this_module_s_scrub_script_byte_for_byte`
  pinned the compaction Dockerfile against `snapshot_scrub_script()`.
  Dropped — it existed only for compaction. `snapshot_scrub_script` and
  its containment tests are untouched.
* `lib.rs`'s startup reap of `:compacting` tags and `triple-c-compact-*`
  containers is dropped: nothing on this branch creates them.
* `project_lock`'s `Compaction` / `CacheClear` variants and
  `any_held_excluding`, `migration_commands::is_migrating`, and
  `formatBytes{Delta,Ceiling}` lose their last production caller but are
  kept and still tested, annotated with why.
* `projects_store::corrupt_since` and `migration_store::peek_ownerless_since`
  were read only by the disk survey and are removed. The corrupt-load
  marker and `.bak` are still written.

Verified: `npm run test` 611 passing, `npx tsc --noEmit` clean,
`npm run build` green; `cargo test` 419 passed / 2 ignored,
`cargo build` 0 warnings. Every test removed belongs to a removed
feature — no kept-behaviour test was weakened or deleted.

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

HOW-TO-USE.md

@@ -1164,8 +1164,10 @@ When you scroll up in the terminal to review previous output, a **Jump to Curren
 The **Files** tab of Project Home browses inside a running container. You can:
 
 - **Browse** the container filesystem, starting at `/workspace`, with breadcrumb navigation
-- **Download** any file to your host machine via the **Download** button on each file entry
-- **Upload file** from your host into the current container directory
+- **Save to host…** — copy any file out to a location you pick. This is the way to get a file out
+  of a container; there is one button per file entry, and the file viewer offers it too
+- **Upload file** from your host into the current container directory — or **drop files straight
+  onto the pane** from your desktop, which uploads them into the directory on screen
 - **Refresh** the directory listing at any time
 
 The listing shows file names, sizes, and modification dates.