COD-121 unified session list: live SSE refresh (slice A, unit 4)

The complete session list now updates live as sessions change, instead of
only on open/welcome-load.

- app.js: extra SSE listeners (session:created/updated/deleted) on the same
  EventSource (multiple listeners per event; existing handlers untouched;
  registered via addListener so they tear down on reconnect) call
  _onSessionListMaybeChanged().
- panels-ui.js: _onSessionListMaybeChanged() debounced-refreshes the Session
  Manager modal when it's open and the welcome list when its overlay is
  visible (no work when neither is showing). _loadSessionManagerList stores the
  active query so refreshes preserve the user's search.

Verified on an isolated beta instance (Playwright): dispatching a session
event refreshes the modal while open, does NOT while closed (gated), and
refreshes the welcome list while visible. Gates: tsc 0, frontend-syntax +
public-asset format clean, build clean.

src/web/public/app.js

@@ -1258,6 +1258,15 @@ class CodemanApp {
     for (const [event] of _SSE_HANDLER_MAP) {
       addListener(event, this._sseHandlerWrappers.get(event));
     }
+
+    // COD-121: live-refresh the unified session list (Session Manager modal +
+    // visible welcome list) on session structural changes. Extra listeners on the
+    // same EventSource — EventSource supports multiple listeners per event — so the
+    // existing handlers above are untouched. Registered through addListener so they
+    // are torn down with the rest on reconnect.
+    for (const event of [SSE_EVENTS.SESSION_CREATED, SSE_EVENTS.SESSION_UPDATED, SSE_EVENTS.SESSION_DELETED]) {
+      addListener(event, () => this._onSessionListMaybeChanged());
+    }
   }
 
   // ═══════════════════════════════════════════════════════════════

src/web/public/panels-ui.js

@@ -338,7 +338,30 @@ Object.assign(CodemanApp.prototype, {
     if (modal) modal.classList.remove('active');
   },
 
+  /**
+   * COD-121: live-refresh the unified session list when sessions change
+   * (created/updated/deleted via SSE). Only touches surfaces that are currently
+   * showing — the open Session Manager modal and/or the visible welcome list —
+   * and is debounced so an event burst collapses into one re-fetch. The current
+   * search query is preserved.
+   */
+  _onSessionListMaybeChanged() {
+    const modal = document.getElementById('sessionManagerModal');
+    if (modal && modal.classList.contains('active')) {
+      this._debouncedCall(
+        'sessionManagerRefresh',
+        () => this._loadSessionManagerList(this._sessionManagerQuery || ''),
+        400
+      );
+    }
+    const welcome = document.getElementById('welcomeOverlay');
+    if (welcome && welcome.classList.contains('visible')) {
+      this._debouncedCall('welcomeHistoryRefresh', () => this.loadHistorySessions(), 600);
+    }
+  },
+
   async _loadSessionManagerList(q = '') {
+    this._sessionManagerQuery = q;
     const list = document.getElementById('sessionManagerList');
     if (!list) return;
     try {