fix(electrobun): address all 22 Codex review #2 findings

CRITICAL:
- DocsTab XSS: DOMPurify sanitization on all {@html} output
- File RPC path traversal: guardPath() validates against project CWDs

HIGH:
- SSH injection: spawn /usr/bin/ssh via PTY args, no shell string
- Search XSS: strip HTML, highlight matches client-side with <mark>
- Terminal listener leak: cleanup functions stored + called in onDestroy
- FileBrowser race: request token, discard stale responses
- SearchOverlay race: same request token pattern
- App startup ordering: groups.list chains into active_group restore
- PtyClient timeout: 5-second auth timeout on connect()
- Rule 55: 6 {#if} patterns converted to style:display toggle

MEDIUM:
- Agent persistence: only persist NEW messages (lastPersistedIndex)
- Search errors: typed error response, "Invalid query" UI
- Health store wired: agent events call recordActivity/setProjectStatus
- index.ts SRP: split into 8 domain handler modules (298 lines)
- App.svelte: extracted workspace-store.svelte.ts
- rpc.ts: typed AppRpcHandle, removed `any`

LOW:
- CommandPalette listener wired in App.svelte
- Dead code removed (removeGroup, onDragStart, plugin loaded)

ui-electrobun/src/mainview/Terminal.svelte

@@ -23,6 +23,8 @@
   let unsubFont: (() => void) | null = null;
   let ro: ResizeObserver | null = null;
   let destroyed = false;
+  // Fix #5: Store listener cleanup functions to prevent leaks
+  let listenerCleanups: Array<() => void> = [];
 
   /** Decode a base64 string from the daemon into a Uint8Array. */
   function decodeBase64(b64: string): Uint8Array {
@@ -126,6 +128,12 @@
     };
     appRpc.addMessageListener('pty.closed', closedHandler);
 
+    // Fix #5: Store cleanup functions for message listeners
+    listenerCleanups.push(
+      () => appRpc.removeMessageListener?.('pty.output', outputHandler),
+      () => appRpc.removeMessageListener?.('pty.closed', closedHandler),
+    );
+
     // ── Send user input to daemon ──────────────────────────────────────────
 
     term.onData((data: string) => {
@@ -148,7 +156,11 @@
     destroyed = true;
     unsubFont?.();
     ro?.disconnect();
-    // Fix #1: Close the PTY session (not just unsubscribe) to prevent session leak
+    // Fix #5: Clean up all message listeners to prevent leaks
+    for (const cleanup of listenerCleanups) {
+      try { cleanup(); } catch { /* ignore */ }
+    }
+    listenerCleanups = [];
     appRpc.request['pty.close']({ sessionId }).catch(() => {});
     term?.dispose();
   });