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/locales/en.json

@@ -662,6 +662,7 @@
     "aiNote": "Nothing is sent anywhere until you add a provider and send a message."
   },
   "nav": {
+    "collab": "Meetings",
     "home": "Home",
     "terminal": "Terminal",
     "localTerminal": "Local Terminal",
@@ -1806,6 +1807,59 @@
     "join": "Join",
     "sharedSessionLabel": "{{hostName}} (shared)"
   },
+  "collab": {
+    "createRoom": "New room",
+    "roomName": "Room name",
+    "persistentRoom": "Persistent room",
+    "persistentRoomHint": "Persistent rooms stay listed after the meeting ends and can be reused.",
+    "noRooms": "No rooms yet. Create one to start a meeting.",
+    "openRoom": "Open",
+    "endRoom": "End meeting",
+    "leaveRoom": "Leave",
+    "deleteMember": "Remove",
+    "invite": "Invite",
+    "inviteTitle": "Invite members",
+    "members": "Members",
+    "online": "online",
+    "hostBadge": "Host",
+    "presenterBadge": "Presenting",
+    "present": "Present",
+    "presentTitle": "Take the stage",
+    "presentHost": "Host",
+    "presentProtocol": "Protocol",
+    "stopPresenting": "Stop presenting",
+    "takeOver": "Take over",
+    "emptyStage": "Nobody is presenting. Take the stage to share a session.",
+    "stageLoading": "Connecting to the stage...",
+    "stageEnded": "The presentation ended",
+    "roomEnded": "This meeting has ended",
+    "presenterLabel": "{{name}} is presenting",
+    "guestLink": "Guest link",
+    "guestLinkOn": "Guest link is on. Anyone with the link can watch the stage.",
+    "guestLinkOff": "Guest link is off.",
+    "copyLink": "Copy link",
+    "linkCopied": "Link copied",
+    "roles": "Roles",
+    "users": "Users",
+    "invitedTo": "You were invited to \"{{name}}\"",
+    "guest": {
+      "title": "Meeting",
+      "waiting": "Waiting for the presenter...",
+      "linkInvalid": "This guest link is invalid or the meeting has ended"
+    },
+    "reopenFromPanel": "This meeting tab expired. Reopen the room from the Meetings panel.",
+    "requestControl": "Request control",
+    "releaseControl": "Release control",
+    "grantControl": "Give control",
+    "revokeControl": "Take back control",
+    "controlRequestedBy": "{{name}} asked for control",
+    "grant": "Grant",
+    "controlBadge": "In control",
+    "youArePresenting": "You are presenting in another tab. Stop presenting to hand the stage over.",
+    "created": "Room created",
+    "invited": "Members invited",
+    "roomTab": "Meeting"
+  },
   "sessionSharing": {
     "guestView": {
       "loading": "Connecting to shared session...",