[modularization] Phase 2: Extract data layer — gitea, weather, bitcoin, loaders

Created modules/data/ with 4 data modules:
- data/gitea.js: Centralized Gitea API (commits, PRs, agent status)
- data/weather.js: Open-Meteo weather data fetch
- data/bitcoin.js: Blockstream block height polling
- data/loaders.js: Static file loaders (portals.json, sovereignty-status.json, SOUL.md)

Updated consumers to use data modules instead of direct fetch():
- panels.js: Uses data/gitea.js for agent status
- heatmap.js: Uses data/gitea.js for commit data
- extras.js: Uses data/gitea.js for timelapse, data/bitcoin.js for block height
- portals.js: Uses data/loaders.js for portals.json
- effects.js: Uses data/loaders.js for sovereignty-status.json
- oath.js: Uses data/loaders.js for SOUL.md
- audio.js: Uses data/loaders.js for SOUL.md

Deduplication wins:
- Gitea token centralized (was hardcoded in 3 files)
- SOUL.md now cached (was fetched 3x independently)
- Nexus commits shared cache (was fetched 2x independently)

Refs #421

modules/data/bitcoin.js

@@ -0,0 +1,27 @@
+// modules/data/bitcoin.js — Blockstream block height polling
+// Writes to S: lastKnownBlockHeight, _starPulseIntensity
+import { S } from '../state.js';
+
+const BITCOIN_REFRESH_MS = 60 * 1000;
+
+export async function fetchBlockHeight() {
+  try {
+    const res = await fetch('https://blockstream.info/api/blocks/tip/height');
+    if (!res.ok) return null;
+    const height = parseInt(await res.text(), 10);
+    if (isNaN(height)) return null;
+
+    const isNew = S.lastKnownBlockHeight !== null && height > S.lastKnownBlockHeight;
+    S.lastKnownBlockHeight = height;
+
+    if (isNew) {
+      S._starPulseIntensity = 1.0;
+    }
+
+    return { height, isNewBlock: isNew };
+  } catch {
+    return null;
+  }
+}
+
+export { BITCOIN_REFRESH_MS };