feat(mcp): generic MCP tool source with per-node function filtering (#301)

* feat(mcp): generic MCP tool source with per-node function filtering

Adds a Model Context Protocol tool category: connect a customer MCP
server and expose its tools to the agent, with optional per-node
allow-listing of individual MCP functions.

- ToolCategory.MCP enum + alembic migration
- MCP definition validator and collision-safe function-name namespacing
- McpToolSession wrapper: graceful-degrade, per-call open/close lifecycle
- CustomToolManager MCP branch (schemas + proxy handlers)
- Per-node mcp_tool_filters threaded through DTO/graph/engine
- Best-effort discovered_tools catalog cache + POST /tools/{uuid}/mcp/refresh
- UI: MCP create/edit config, tabbed ToolSelector with per-node toggles

* feat: refactor for code standardisation and documentation

---------

Co-authored-by: Abhishek Kumar <abhishek@a6k.me>

api/Dockerfile

@@ -20,7 +20,7 @@ RUN pip install --user --no-cache-dir -r requirements.txt && \
 
 # Copy and install pipecat from local submodule
 COPY pipecat /tmp/pipecat
-RUN pip install --user --no-cache-dir '/tmp/pipecat[cartesia,deepgram,openai,elevenlabs,groq,google,azure,sarvam,soundfile,silero,webrtc,speechmatics,openrouter,camb]' && \
+RUN pip install --user --no-cache-dir '/tmp/pipecat[cartesia,deepgram,openai,elevenlabs,groq,google,azure,sarvam,soundfile,silero,webrtc,speechmatics,openrouter,camb,mcp]' && \
     # Swap opencv-python (pulled by pipecat[webrtc]) for opencv-python-headless
     # to drop X11/Qt dependencies that otherwise require libxcb etc. in runner.
     pip uninstall -y opencv-python && \