fix: stabilize CI — TS widen, sys.modules restore, WS subscriber race (#17836)

Three narrow fixes targeting the remaining red checks after #17828:

1. ui-tui/src/app/slash/commands/ops.ts (Docker Build):
   /reload-mcp's local params type annotated session_id: string
   while ctx.sid is string | null. Widen to string | null —
   matches every other rpc call site and the test harness which passes
   { session_id: null }. Fixes TS2322 on line 86. The rpc signature
   itself is Record<string, unknown>, so this is purely a local
   typing fix, no behavioral change.

2. tests/plugins/test_achievements_plugin.py (13 cascading test failures):
   _install_fake_session_db did a raw sys.modules['hermes_state'] =
   fake_module without restoration, leaking the fake across xdist
   worker boundaries. Downstream tests doing from hermes_state import
   SessionDB got a module whose SessionDB was lambda: fake_db
   — 6 test_hermes_state.py tests failed with AttributeError: 'function'
   object has no attribute '_sanitize_fts5_query' / _contains_cjk,
   and 7 test_860_dedup.py tests failed with TypeError: got unexpected
   keyword argument 'db_path' (real code calls SessionDB(db_path=...)).

   Fix: stash monkeypatch on the plugin_api module object in the
   fixture, and have the helper do monkeypatch.setitem(sys.modules,
   'hermes_state', fake_module) for auto-restoration at test teardown.

3. tests/hermes_cli/test_web_server.py (WS race):
   TestPtyWebSocket::test_pub_broadcasts_to_events_subscribers hit the
   30s test timeout on CI. websocket_connect returns after
   ws.accept() — but /api/events registers the subscriber in
   _event_channels on the NEXT await (inside _event_lock). A
   publish immediately after connect could race ahead of registration
   and be dropped, and the subsequent receive_text() blocked until
   SIGALRM killed the test. Fix: poll _event_channels after the
   subscriber connects, before publishing.

Validation:
scripts/run_tests.sh tests/plugins/test_achievements_plugin.py
                     tests/run_agent/test_860_dedup.py
                     tests/test_hermes_state.py
                     tests/hermes_cli/test_web_server.py    338 passed
cd ui-tui && npm run type-check                             clean
cd ui-tui && npm run build                                  clean

Remaining red checks are pure infra (Nix ubuntu hits
TwirpErrorResponse ResourceExhausted on the GH Actions cache API; Nix
macos bounces between npm build openssl-legacy and cache rate-limits)
and cannot be fixed in the codebase.

tests/plugins/test_achievements_plugin.py

@@ -50,6 +50,12 @@ def plugin_api(tmp_path, monkeypatch):
     )
     module = importlib.util.module_from_spec(spec)
     spec.loader.exec_module(module)
+    # Stash monkeypatch so ``_install_fake_session_db`` can use it to
+    # swap ``sys.modules['hermes_state']`` with auto-restoration. Without
+    # this, a raw ``sys.modules[...] = fake`` assignment would leak the
+    # fake into later tests in the same xdist worker — breaking every
+    # test that does ``from hermes_state import SessionDB``.
+    module._test_monkeypatch = monkeypatch
     yield module
 
 
@@ -107,10 +113,15 @@ class _FakeSessionDB:
 
 
 def _install_fake_session_db(plugin_api, fake_db):
-    """Inject a fake SessionDB so ``scan_sessions`` finds it via its local import."""
+    """Inject a fake SessionDB so ``scan_sessions`` finds it via its local import.
+
+    Uses the monkeypatch stashed on ``plugin_api`` by the fixture, so the
+    ``sys.modules['hermes_state']`` swap is auto-restored at test teardown
+    and cannot leak into unrelated tests in the same xdist worker.
+    """
     fake_module = type(sys)("hermes_state")
     fake_module.SessionDB = lambda: fake_db
-    sys.modules["hermes_state"] = fake_module
+    plugin_api._test_monkeypatch.setitem(sys.modules, "hermes_state", fake_module)
 
 
 def test_scan_sessions_default_scans_all_history_not_first_200(plugin_api):