fix: prevent infinite loading screen by adding sweep timeouts

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>

server.mjs

@@ -408,7 +408,7 @@ async function start() {
     process.exit(1);
   });
 
-  server.on('listening', () => {
+  server.on('listening', async () => {
     console.log(`[Crucix] Server running on http://localhost:${port}`);
 
     // Auto-open browser
@@ -420,17 +420,18 @@ async function start() {
       if (err) console.log('[Crucix] Could not auto-open browser:', err.message);
     });
 
-    // Try to load existing data first for instant display
+    // Try to load existing data first for instant display (await so dashboard shows immediately)
     try {
       const existing = JSON.parse(readFileSync(join(RUNS_DIR, 'latest.json'), 'utf8'));
-      synthesize(existing).then(data => {
-        currentData = data;
-        console.log('[Crucix] Loaded existing data from runs/latest.json');
-        broadcast({ type: 'update', data: currentData });
-      }).catch(() => {});
-    } catch { /* no existing data */ }
+      const data = await synthesize(existing);
+      currentData = data;
+      console.log('[Crucix] Loaded existing data from runs/latest.json — dashboard ready instantly');
+      broadcast({ type: 'update', data: currentData });
+    } catch {
+      console.log('[Crucix] No existing data found — first sweep required');
+    }
 
-    // Run first sweep
+    // Run first sweep (refreshes data in background)
     console.log('[Crucix] Running initial sweep...');
     runSweepCycle().catch(err => {
       console.error('[Crucix] Initial sweep failed:', err.message || err);