feat(queue): server-side PTY-inject + idle-drained follow-up queue (W2)

The walk-away primitive: queue follow-up prompts and let a session advance itself
while you're gone — "run the tests" drains, and when Claude next goes idle "open a
PR" drains. Injection reuses writeInput (byte-identical to a keystroke, broadcasts
to all mirrored devices); the byte-shuttle is untouched.

- POST/GET/DELETE /live-sessions/:id/queue — POST/DELETE behind requireAllowedOrigin
  + a per-IP rate limit (QUEUE_RATE_MAX=20/min) + SESSION_ID_RE; text non-empty,
  byte-capped (QUEUE_ITEM_MAX_BYTES=4096, 16kb body), count-capped (QUEUE_MAX_ITEMS=10).
- Bounded per-session queue in manager (enqueueFollowup/drainOne/clearQueue);
  new optional queueLength on LiveSessionInfo.
- Idle drain: the Stop/SessionEnd /hook branch scheduleDrain()s a debounced timer
  (QUEUE_SETTLE_MS=1500). It drains exactly one entry only if the session still
  exists, hasn't exited, produced no output during settle, and is idle — three
  guards (debounced single timer + pop-one + settle re-check) → one entry per idle.
- New additive ServerMessage {type:'queue',length} broadcasts the count to mirrors
  (⧗N badge); FE enqueue via the quick-reply editor + TabApp.enqueueToActive.

Injected bytes go verbatim to the PTY (never built into a shell command). Verified
independently: typecheck + build:web clean, 1737 tests pass (real-PTY integration
covers idle-drain / one-per-idle / settle-guard). Foundation for templated launches,
auto-continue, and issue-intake (docs/ROADMAP.md).

vitest.config.ts

@@ -24,6 +24,7 @@ export default defineConfig({
         'src/**/*.ts',
         'public/terminal-session.ts',
         'public/link-paths.ts',
+        'public/queue.ts',
         'public/tabs.ts',
         'public/grid-layout.ts',
         'public/grid-presets.ts',