fix(frontend): surface daemon failure reason instead of generic "not ready" error

[xOAviOx]

Bug

When a second checkout's Electron instance cannot attach to the daemon (checkout identity mismatch — but also spawn failure or unexpected exit), the main process computes a specific, actionable diagnostic and sends it over the daemon:status IPC. The renderer drops it: every API call surfaces only the generic "AO daemon is not ready." error, so the user never learns another checkout owns the daemon or how to fix it.

Root cause

• applyDaemonStatus() (renderer/lib/daemon-status.ts) quarantines the base URL for non-ready statuses but discards status.message.
• runtimeFetch()'s 503 short-circuit (renderer/lib/api-client.ts) hardcodes the generic body, so apiErrorMessage() can only ever surface the fallback.

The diagnostic is computed in main.ts (daemonIdentityError()), shipped over IPC, and then dead on arrival.

Fix

Keep the status message alongside the quarantined base URL (setDaemonUnavailableMessage), and let the 503 short-circuit prefer it over the generic fallback — the same status.message || "AO daemon is not ready." pattern _shell.tsx already uses for project creation. This benefits every daemonStatus failure path (identity mismatch, spawn failure, daemon exit), not just the issue's trigger, and complements #2253 (which disables actions and adds a Restart button but does not fix the message masking).

Testing

• New renderer/lib/daemon-status.test.ts regression test: fails before the fix (generic message masks the identity diagnostic), passes after. Also covers the no-message fallback and that a stale reason is cleared once the daemon is ready again.
• useDaemonStatus.test.tsx: completed the partial api-client mock with the new export.
• Full frontend vitest suite, tsc --noEmit, and prettier --check on the changed files all pass.

Fixes #2481

[somewherelostt]

Thanks for contributing to Agent Orchestrator.

This PR is being picked up by the current external contributor on-call pair:

• @neversettle17-101
• @somewherelostt

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