M9: a joined live session keeps reconnecting and says when it's disconnected

A session you joined could end for reasons that pass, or after about 85 s of
retries, and its tab then looked like an unsaved local file. Work done there
reached no one, with only a 3 s toast to say so.

A live connection now reconnects until you leave, pausing a minute after each
12 attempts. Only refusals that are for good stop it, so "too many messages",
"busy" and the like retry. Messages queued while offline go out paced so a long
queue can't trip the server's rate limit. A session that ended stays on its tab:
the tab shows a red mark and a strip across the canvas offers Retry now or Try
again, Save a copy and Dismiss. Joining again uses the same tab, and what changed
offline opens beside it as an unsaved copy. A session that gets out of step
joins again by itself.

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

docs/server.md

@@ -43,7 +43,7 @@ Releases also ship it ready-built for Linux (`figcraft-server-<version>-linux-x8
   tells everyone it is restarting. Every change it accepted is on disk before anyone is told about
   it, so even a hard kill loses nothing confirmed (a file's log is then folded into a new snapshot
   the next time everyone leaves it). Apps that were in a file keep editing and reconnect once the
-  server is back (for about a minute and a half), as the same participants.
+  server is back, as the same participants.
 
 ## Publishing a file