feat(ui,desktop): explain a red connection dot, follow the project in use, normalize OSC loopback

[pyramation]

Summary

Three failure modes that were all silent: a red dot with no reason, a "running" show with nothing listening, and OSC packets dropped into the void.

The dot now diagnoses itself. useSocket threw the close code away, never retried, and rendered one boolean. It now probes the two endpoints that separate the possible causes and reconnects with backoff:

/api/config unreachable  → serverUnreachable  "Can't reach the server — the show may be stopped."
/api/config !ok          → serverUnreachable  "HTTP <status>"
/api/me 401 (or no token)→ sessionExpired     "sign in again"
both ok, code 1000/1001  → closed             (server restarting)
both ok, any other code  → rejected           (JWT secret changed)

retryDelay(n) = min(500 * 2^(n-1), 10_000)

Amber while connecting/reconnecting, red once down, and the reason renders next to it. StatusDot is the only UI addition — the dot's position, size and colours are unchanged.

Startup failures now reach the operator. startServer only called listen, which is async, so a port clash produced a show that reported running while nothing was bound — the actual cause of a red dot with no explanation. ServerHandle gains ready, the brain awaits it, and both the CLI (awaitBind) and the desktop surface the message. BrainStatus carries the outcome instead of it dying in a console:

+ receiverError: string | null;  // brain is up, but nothing reaches the lasers
+ lastError: string | null;      // why the last start attempt failed

Receiver failure stays non-fatal (the show still runs console-only) but is now reported as its own amber warning rather than looking healthy.

"Use project" moves every panel. Project-scoped hooks refetch on their project argument, but two things didn't follow: a project pinned by Config on a row kept overriding the active one, and the embedded artist UI is served on the same origin whichever project runs, so its WebContentsView never reloaded. projects:use now drops the pin and restarts a live brain onto the new project; brain:start invalidates the laser view. Saving config does the same, since the brain resolves its config once at startup. did-fail-load also clears loadedUrl so a failed first load isn't remembered as loaded.

OSC loopback. OSC is UDP, so a wrong host fails with no error at all — and localhost is the trap: it can resolve to IPv6 ::1 while BEYOND/FB4 listens on IPv4. normalizeOscHost rewrites every loopback alias to 127.0.0.1 wherever a host is stored (CLI wizard, flags, desktop), the BEYOND wizard defaults to it, and the Output route gets a This machine button plus a ? explaining host vs. LAN IP.

Receiver, socket and OSC protocols are untouched.

Link to Devin session: https://app.devin.ai/sessions/972698f89f494b86828010666a002b8f
Requested by: @pyramation

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