feat: collaboration rooms with switchable presenter (#1328)

* feat: add collaboration rooms with switchable presenter

Rooms are a group of members watching one stage - the live SSH/RDP/VNC
session the current presenter shares. Any member can take over the
stage; the host can invite, force-stop and end the meeting. Stages
reuse session_shares (new room share type), so gating, recording,
expiry and the global sharing toggle all apply unchanged.

* feat: add stage control handoff to collaboration rooms

The presenter or host can grant any member write access to the live
stage and take it back; members can raise a hand to ask. SSH flips the
participant's permission on the live gate; RDP/VNC re-mint the viewer's
join token. Control clears on every stage switch.

* feat: guest links, role invites and invite awareness for collab rooms

- Anonymous guest link per room (host toggles/rotates), followed by
  polling the public resolve endpoint; SSH guests join over the terminal
  WS with roomGuestToken, guac guests get read-only join tokens
- Invite by role (expands to current members, snapshot semantics)
- Toast when a room you were invited to appears
- Stale stages are cleared lazily when the presenter is gone
- Telnet presenting, expired-tab fallback, documented single-instance
  and guac-kick limits
- Tests for the collab routes, room hub, share access and control flip

* fix: keep remote desktop collaboration read-only

src/ui/sidebar/rail-items.ts

@@ -19,6 +19,7 @@ import {
   User,
   Workflow,
   Zap,
+  Presentation,
   type LucideIcon,
 } from "lucide-react";
 import { isElectron } from "@/lib/electron";
@@ -83,6 +84,12 @@ export const RAIL_ITEMS: RailItemDef[] = [
     separatorAfter: true,
     rightDockable: true,
   },
+  {
+    id: "collab",
+    icon: Presentation,
+    labelKey: "nav.collab",
+    separatorAfter: true,
+  },
   {
     id: "quick-connect",
     icon: Zap,