feat: add Discord integration with chat_bridge abstraction layer

Introduces a vendor-agnostic chat platform architecture:

- chat_bridge/base.py: ChatPlatform ABC, ChatMessage, ChatThread
- chat_bridge/registry.py: PlatformRegistry singleton
- chat_bridge/invite_parser.py: QR + Ollama vision invite extraction
- chat_bridge/vendors/discord.py: DiscordVendor with native threads

Workflow: paste a screenshot of a Discord invite or QR code at
POST /discord/join → Timmy extracts the invite automatically.

Every Discord conversation gets its own thread, keeping channels clean.
Bot responds to @mentions and DMs, routes through Timmy agent.

43 new tests (base classes, registry, invite parser, vendor, routes).

https://claude.ai/code/session_01WU4h3cQQiouMwmgYmAgkMM

pyproject.toml

@@ -54,6 +54,12 @@ voice = [
 telegram = [
     "python-telegram-bot>=21.0",
 ]
+# Discord: bridge Discord messages to Timmy with native thread support.
+# pip install ".[discord]"
+# Optional: pip install pyzbar Pillow  (for QR code invite detection)
+discord = [
+    "discord.py>=2.3.0",
+]
 # Creative: GPU-accelerated image, music, and video generation.
 # pip install ".[creative]"
 creative = [
@@ -84,6 +90,7 @@ include = [
     "src/notifications",
     "src/shortcuts",
     "src/telegram_bot",
+    "src/chat_bridge",
     "src/spark",
     "src/tools",
     "src/creative",