feat: Add E2E encryption support to Matrix bot

- matrix-nio[e2e] with libolm for Megolm encryption
- Persistent crypto store volume for key persistence
- Auto-accept key verification (SAS)
- Upload device keys on first login

CF-1147

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

requirements.txt

@@ -4,4 +4,4 @@ livekit-plugins-elevenlabs>=1.4,<2.0
 livekit-plugins-silero>=1.4,<2.0
 livekit>=1.0,<2.0
 livekit-api>=1.0,<2.0
-matrix-nio>=0.25,<1.0
+matrix-nio[e2e]>=0.25,<1.0