fix(git): bound status payload and repo discovery; add reset escape hatch (#369)

Opening the source-control panel could freeze the whole sidebar, and the
frozen layout restored itself after every reload, leaving no way out
(issue #369). Three unbounded layers compounded:

- `git status --porcelain -z --untracked-files=all` shipped every row of a
  pathological untracked set into one response; the browser main thread
  froze on response.json() plus the unvirtualized change list, and the 2s
  poll replayed the freeze. status() now caps entries at 2000 and reports
  `truncated` (the panel shows a notice, mirroring fs.read's truncation
  semantics); worktree change counts inherit the bound for free.
- repoRoots() probed every visible child directory of a non-repo cwd
  (e.g. ~) serially, once per git.* call, each with the full 30s command
  budget. Discovery now uses a 3s probe timeout, caps probes at 200
  directories, and shares one in-flight scan plus a 60s TTL cache per cwd.
- A hung layout persisted `panelOpen: true` with the git tab active, so a
  reload remounted straight back into the freeze with no escape hatch.
  Loading with `?dsh-sidebar-reset` now drops the persisted layout (and
  the shared width) and starts from the default.

statusTruncated copy synced across all 19 shipped dictionaries.

src/client/api.ts

@@ -44,6 +44,9 @@ export interface GitStatusResult {
   isRepo: boolean
   branch?: string
   entries: GitStatusEntry[]
+  /** True when the host capped `entries` (huge untracked set); the panel
+   *  shows a truncation notice instead of freezing (#369). */
+  truncated?: boolean
   root?: string
   repositories?: string[]
 }