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

drizzle/mysql/0016_unusual_tyrannus.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `collab_rooms` ADD `guest_link_token` varchar(255);--> statement-breakpoint
+ALTER TABLE `collab_rooms` ADD CONSTRAINT `idx_collab_rooms_guest_token` UNIQUE(`guest_link_token`);