Add shared-auth-token UI and make cancelling actually cancel

UI for the shared Claude token: a Settings section showing token state
with Authenticate and Revoke, an acquisition modal built on the shared
Modal (sign-in link handed to the host browser via the opener plugin,
plus the code input that answers `setup-token`'s stdin prompt — the flow
cannot complete without it), and a per-project opt-out toggle shown only
for the Anthropic backend.

Cancellation: acquire_claude_token previously had only two exits,
completion and a 15-minute timeout, and held the single-flight guard for
the whole time. Closing the dialog therefore locked the user out of
retrying for up to 15 minutes. Adds cancel_claude_token, backed by a
oneshot claimed and released in lockstep with the input guard, selected
on in the run loop so it wins the race and tears the exec down. The
dialog's Cancel now calls it and closes either way.

Also refreshes CLAUDE.md, which had drifted: it documented the deleted
ProjectCard, and asserted that new IPC commands need permission grants
in capabilities/default.json — they do not, that file covers plugin
commands only. Adds the conventions that would otherwise bite:
container_needs_recreation() is purely label-based and never diffs env,
so container-affecting state needs its own label; and #[serde(default)]
on a bool yields false regardless of intent.

Corrects the claim that Reset preserves credentials. Reset calls
remove_project_volumes, which deletes both the home and claude-config
volumes, so it wipes ~/.claude, the OAuth token, installed skills and
session transcripts.

84 frontend tests, 34 Rust tests, both builds clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/hooks/useClaudeAuth.test.ts

@@ -0,0 +1,61 @@
+import { describe, it, expect } from "vitest";
+import { authErrorMessage, extractSignInUrl } from "./useClaudeAuth";
+
+describe("extractSignInUrl", () => {
+  it("finds the authorize URL in realistic setup-token output", () => {
+    const url =
+      "https://claude.ai/oauth/authorize?code=true&client_id=abc&redirect_uri=https%3A%2F%2Fplatform.claude.com%2Foauth%2Fcode%2Fcallback";
+    expect(
+      extractSignInUrl(
+        `Claude Code long-lived token setup\nBrowser didn't open? Use this url to sign in:\n${url}\n\nPaste code here if prompted > `,
+      ),
+    ).toBe(url);
+  });
+
+  it("returns null before the CLI has printed anything useful", () => {
+    expect(extractSignInUrl("")).toBeNull();
+    expect(extractSignInUrl("Starting `claude setup-token`…\n")).toBeNull();
+  });
+
+  it("drops trailing prose punctuation", () => {
+    expect(extractSignInUrl("Visit https://claude.ai/oauth/authorize?x=1.")).toBe(
+      "https://claude.ai/oauth/authorize?x=1",
+    );
+  });
+
+  it("prefers the OAuth URL over unrelated links in the transcript", () => {
+    const text =
+      "Docs: https://docs.claude.com/en/docs/claude-code/setup-token-and-more-words\n" +
+      "Sign in: https://claude.ai/oauth/authorize?code=true\n";
+    expect(extractSignInUrl(text)).toBe("https://claude.ai/oauth/authorize?code=true");
+  });
+
+  it("keeps the full link when a TUI repaint also emitted a truncated one", () => {
+    const full = "https://claude.ai/oauth/authorize?code=true&client_id=abcdefgh";
+    const text = `https://claude.ai/oauth/authorize?code=tr\n${full}\n`;
+    expect(extractSignInUrl(text)).toBe(full);
+  });
+});
+
+describe("authErrorMessage", () => {
+  it("passes a Tauri string rejection through verbatim", () => {
+    const backend =
+      "The container for 'api' is not running. Start it, then run authentication again.";
+    expect(authErrorMessage(backend, "fallback")).toBe(backend);
+  });
+
+  it("uses an Error's message", () => {
+    expect(authErrorMessage(new Error("channel closed"), "fallback")).toBe(
+      "channel closed",
+    );
+  });
+
+  it("falls back rather than stringifying an opaque value", () => {
+    expect(authErrorMessage({ weird: true }, "Something went wrong.")).toBe(
+      "Something went wrong.",
+    );
+    expect(authErrorMessage("   ", "Something went wrong.")).toBe(
+      "Something went wrong.",
+    );
+  });
+});