fix(remote): make the wake banner's poller page-wide and independent of tab switches

Reported as 'the tab shows no banner' while the host was verifiably unreachable: the
banner only started polling from selectSession, which RETURNS EARLY for the tab you
are already on (so a page loaded with the remote tab active never polled), and a
long-lived tab keeps running the JS it loaded — the feature was invisible to anyone
who did not switch tabs after the deploy.

The poller is now page-wide: one interval (created on init and on the first session
switch), re-targeted whenever the active session changes, plus a visibilitychange
wake-up. It no longer depends on any single selection path running.

Also adds test/sse-dispatch-table.test.ts: a static guard that every
[SSE_EVENTS.X, '_onFoo'] entry names an event constants.js defines AND a handler some
module defines. Both halves fail silently (a typo'd constant is an undefined table
key; a renamed handler just never runs), which is exactly how a new banner can never
appear with no error anywhere.

src/web/public/app.js

@@ -1815,6 +1815,9 @@ class CodemanApp {
   _onInit(data) {
     _crashDiag.log(`INIT: ${data.sessions?.length || 0} sessions`);
     this.handleInit(data);
+    // Start the remote-host reachability poller even if no session switch follows
+    // (a page loaded with the remote tab already active) — see host-wake-ui.js.
+    this._ensureHostWakePoller?.();
   }
 
   _onSessionCreated(data) {