The dashboard would hang indefinitely on the loading screen because:
1. `bls.mjs` used a raw `fetch()` without any timeout/AbortSignal —
if the BLS API was slow or unresponsive, it would block forever.
2. `runSource()` in `briefing.mjs` had no per-source timeout, so a
single hanging API could stall the entire sweep indefinitely.
3. `server.mjs` loaded cached `latest.json` via a fire-and-forget
promise (`.then()`) instead of `await`, meaning the dashboard
never received the cached data before the sweep started.
4. `loading.html` relied solely on SSE for redirect — if the SSE
connection missed the update event, the page would never redirect.
Changes:
- Add 15s AbortController timeout to BLS `getSeries()` fetch call
- Add 30s per-source timeout via `Promise.race()` in `runSource()`
- Await `synthesize()` when loading cached data so the dashboard
serves instantly on restart when `runs/latest.json` exists
- Add 5s fallback polling to loading page alongside SSE
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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