fix(tts): real Persian Gemini speech on Cloudflare runtime

[AmirMotefaker]

Implements Issue #65 and fixes the real-browser stable blocker found during Issue #61.

Root cause

The preview Worker intentionally returned HTTP 503 for every /api/tts call, so Chrome had to fall back to Web Speech. On the tested Windows Chrome environment no usable fa/fa-IR voice exists, making speech acceptance impossible.

Fix

• real Gemini TTS in cloudflare/worker.mjs;
• female Sulafat and male Iapetus preserved;
• Persian narration is chunked and returned as audio/wav;
• voice name/gender response headers exposed to the extension;
• GEMINI_API_KEY is bound only to the isolated Cloudflare Worker, never bundled into the extension;
• /health now reports actual Gemini speech readiness;
• deployment gate now requires a real female + male Persian audio E2E instead of accepting the old 503 browser-fallback contract.

Safety

• Draft PR;
• no stable release;
• no store submission;
• production Farsio website untouched;
• browser fallback remains secondary only.

After CI passes, Cloudflare preview must prove real audio E2E before merge. Then a new exact-main stable candidate will be generated for Chrome/Edge acceptance.

Refs #65 #61