Surface structured RCON failure reasons in the fleet UI

rconGetStatus previously collapsed at least five distinct failure modes
(no password, no port, socket error, timeout, bad reply) into a single
null return, so the UI could only say "rcon unreachable" — useless when
diagnosing a real Alcatraz outage.

Refactored to rconStatusResult() returning a discriminated union with a
RconFailure reason and human-facing detail. The worker persists these as
"<reason>:<detail>" in last_error (no schema change). /api/servers now
returns the derived endpoint (host:port) per server plus a top-level
integrations block (rcon/komodo configured, timeout, default host).

Server detail page gains an RCON diagnostic panel when health is not
online: shows the exact endpoint being dialed, integration status,
timeout, a color-coded reason tag, the detail, and a targeted fix hint.
Wrong-password replies are detected via "bad rcon" text in the print
body.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/routes/+page.svelte

@@ -19,6 +19,7 @@
         last_error: string | null;
         roster: RosterPlayer[] | null;
         health: Health;
+        endpoint: { host: string; port: number } | null;
         held: HeldRow[];
     }