Stop the admin panel hanging when slskd is down

/api/admin/system probed slskd with the shared client, whose 30s timeout is
sized for searches and transfers. So the panel sat on skeletons for the full
30s exactly when slskd was unreachable -- the case you open it to diagnose --
and the 5s UI poll stacked requests behind it. Probes now get 4s: above a LAN
round-trip, under the poll interval.

httpx.ConnectTimeout also stringifies to "", so the banner rendered
"slskd unreachable -- " with nothing after the dash. Fall back to the
exception class name.

Add dev.sh, because the documented dev commands could not work: MUSE_DB
defaults to /config/muse.db which a Mac cannot write, and the auth preflight
refuses to boot without a client ID.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -4,3 +4,4 @@ config/
 *.db
 .venv/
 .DS_Store
+dev/