Invite links: starsync:// opens the app and asks to join; one app per profile; real invite address; clipboard pick-up

- starsync://host:port/?name=&pw= (PROTOCOL.md "Invite link"); the password only when ticked, never in logs
- Linux: launcher entry takes x-scheme-handler/starsync (%u, StartupNotify) and becomes its xdg-mime default; Windows: HKCU\Software\Classes\starsync -> starsync.exe
- InstanceLock: lock file + loopback handoff per profile folder; the running app comes up with the second start's activation token (Wayland/X11) or AllowSetForegroundWindow (Windows)
- Sharing looks up the internet address (HTTPS services with fallbacks); members card picks Internet / Home network / VPN and says when the port needs forwarding
- JoinOffers: link and clipboard prompt with /health, joins through ConnectFlow; dismissed clipboard invites kept as fingerprints

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/HOW-IT-WORKS.md

@@ -45,7 +45,9 @@ A five-minute tour. Details: [ARCHITECTURE.md](ARCHITECTURE.md), wire format:
   not in a friend's, so watching alone works like a session (progress,
   next episode). Invite opens it to friends on your network (a second
   listener on the same server: nothing restarts, the video and Up next
-  carry on) and copies an invite; Stop sharing closes it again.
+  carry on) and copies an invite link (`starsync://`, with your internet
+  address when the app finds it); Stop sharing closes it again. A friend
+  clicks the link, or just copies it, and their app asks to join.
 - **Dedicated server**: `starsync-server`, a separate program in the
   release tarball, for an always-on box. See the README.