feat(e2ee): Add HKDF E2EE support for Element Call compatibility

Element Call uses HKDF-SHA256 + AES-128-GCM for frame encryption,
while the LiveKit Rust SDK defaults to PBKDF2 + AES-256-GCM.

- Multi-stage Dockerfile builds patched Rust FFI from EC-compat fork
- Generates Python protobuf bindings with new fields
- patch_sdk.py modifies installed livekit-rtc for new proto fields
- agent.py passes E2EE options with HKDF to ctx.connect()
- bot.py exchanges encryption keys via Matrix state events
- Separate Dockerfile.bot for bot service (no Rust build needed)

Ref: livekit/rust-sdks#904, livekit/python-sdks#570

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

docker-compose.yml

@@ -1,13 +1,17 @@
 services:
   agent:
-    build: .
+    build:
+      context: .
+      dockerfile: Dockerfile
     command: python agent.py start
     env_file: .env
     restart: unless-stopped
     network_mode: host
 
   bot:
-    build: .
+    build:
+      context: .
+      dockerfile: Dockerfile.bot
     command: python bot.py
     env_file: .env
     restart: unless-stopped