fix: keep a remote session's fix plan authoritative (release review, #722)

#722 stopped handing a remote session's workingDir to the Ralph tracker,
which also left isFileAuthoritative false for remote sessions only. That
flag is what keeps the output-based completion guessers off, and it is
true for every local session with a working directory, so a remote loop
could end, and mark every todo done, on a prose line such as "All tasks
completed" while a local one cannot.

setRemoteWorkingDir() records the path without reading or watching the
local disk, so the fix plan stays authoritative as for a local session;
the file still reaches the tracker only through fix-plan/read, over ssh.
The test pins both, and fails on the previous head.

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

docs/remote-sessions.md

@@ -432,9 +432,12 @@ path but the SESSION (`session.remote`): a remote session never falls back to lo
 records, which are keyed to the session that registered them.
 
 **Local watchers skip a remote session.** The Ralph tracker's `@fix_plan.md` auto-load
-(and the `fs.watch` behind it) never runs for a remote session: `setupSessionListeners()`
-(`server.ts`) does not hand the tracker a remote `workingDir`, because the watcher reads
-the LOCAL disk, where that path is missing or a different tree.
+(and the `fs.watch` behind it) never runs for a remote session, because the watcher reads
+the LOCAL disk, where that path is missing or a different tree: `setupSessionListeners()`
+(`server.ts`) calls `setRemoteWorkingDir()` instead, which only records the path. The fix
+plan stays authoritative exactly as for a local session, so the tracker's output-based
+completion guessers stay off there too; the file reaches the tracker only through
+`fix-plan/read`, over ssh. The image watcher skips remote sessions the same way.
 
 ## Wake-on-LAN from user input