Remove unused isCacheAvailable() export (AI)

Dead code -- nothing in the codebase imported or called it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AXSVPS3UmmASiiprPfcnUd

js/cache.js

@@ -61,10 +61,6 @@ async function runRequest(mode, makeRequest) {
     }
 }
 
-export function isCacheAvailable() {
-    return cacheAvailable;
-}
-
 // Returns every cached { path, mtime, article } record as a Map keyed by
 // path — one bulk read instead of a separate IndexedDB round-trip per
 // article file, which matters once there are hundreds of them: discovery.js