browser relay: multi-session override, stale session recovery, better error feedback

- relay accepts new extension connections by closing old one (last wins, code 4000)
- extension recognizes code 4000 and stops auto-reconnect (shows "replaced" badge)
- fix ping interval race where old WS close handler killed new connection's pings
- retry CDP commands on "Session with given id not found" by re-attaching debugger
- describeError() maps known errors to user-friendly badge tooltips
- persisted relay tokens restored on server start
- user-scoped token salts, token regeneration/deletion endpoints
- extension download endpoint, integrations UI for browser relay setup
- browser relay env vars passed to pi-bridge sandboxes
- browser screen layout with chat panel and prompt prefix

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/apps/officer-web/Screens/Dashboard/Browser/defaultLayout.ts

@@ -6,6 +6,17 @@ export const defaultLayout: LayoutNode = {
   direction: 'horizontal',
   children: [
     { node: { type: 'panel', id: 'browser-tabs', appType: null }, size: 25 },
-    { node: { type: 'panel', id: 'browser-preview', appType: null }, size: 75 },
+    {
+      node: {
+        type: 'group',
+        id: 'browser-right',
+        direction: 'vertical',
+        children: [
+          { node: { type: 'panel', id: 'browser-preview', appType: null }, size: 60 },
+          { node: { type: 'panel', id: 'browser-chat', appType: 'officerdev/chat' }, size: 40 },
+        ],
+      },
+      size: 75,
+    },
   ],
 };