fix(browse): daemon resilience on loaded machines — Bun conn errors, stop/restart flush, startup + git-root budgets

Four load-sensitivity fixes in the daemon lifecycle:

- sendCommand only recognized Node's ECONNREFUSED/ECONNRESET; the compiled
  CLI runs on Bun, which reports 'ConnectionRefused'/'ConnectionClosed'
  ("Unable to connect..."), so daemon crashes leaked the raw error and
  exited 1 instead of entering the busy-check/restart path. Match both.
- stop/restart called shutdown() inline, which exits before the HTTP
  response flushes — the CLI saw a dropped socket (and would now
  crash-retry a fresh daemon just to stop it). Defer shutdown ~100ms so
  the 200 lands first.
- Non-CI POSIX startup budget raised 8s -> 15s (cold Chromium measured
  ~5.7s at load avg 10; load 12+ blew the old budget while the detached
  daemon was still booting).
- getGitRoot's 2s git rev-parse timeout returned null under load (6.3s
  spikes measured), scattering state files across cwds into split-brain
  daemons. Raise to 8s, still bounded.

Contributed by @mplatts (PR #1732).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

browse/test/commands.test.ts

@@ -884,7 +884,10 @@ describe('CLI lifecycle', () => {
     cliEnv.BROWSE_STATE_FILE = stateFile;
     const result = await new Promise<{ code: number; stdout: string; stderr: string }>((resolve) => {
       const proc = spawn('bun', ['run', cliPath, 'status'], {
-        timeout: 15000,
+        // Must exceed the CLI's startup budget (resolveStartTimeout, 15s
+        // non-CI POSIX) or a slow cold boot under full-suite load gets the
+        // child killed at the exact moment the CLI would have succeeded.
+        timeout: 18000,
         env: cliEnv,
       });
       let stdout = '';