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/locales.ts

@@ -110,6 +110,7 @@ export const zh = {
   splitDown: '向下分栏',
   notRepo: '当前目录不是 git 仓库',
   noChanges: '没有变更',
+  statusTruncated: '变更过多，仅显示前 2000 条',
   stage: '暂存',
   unstage: '取消暂存',
   stageAll: '全部暂存',
@@ -453,6 +454,7 @@ export const en: Record<keyof typeof zh, string> = {
   splitDown: 'Split down',
   notRepo: 'This directory is not a git repository',
   noChanges: 'No changes',
+  statusTruncated: 'Too many changes; showing the first 2,000 entries',
   stage: 'Stage',
   unstage: 'Unstage',
   stageAll: 'Stage all',