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/services/workflow/pipecat_engine_context_composer.py

@@ -117,7 +117,8 @@ async def compose_functions_for_node(
     # Custom tools
     if node.tool_uuids and custom_tool_manager:
         custom_tool_schemas = await custom_tool_manager.get_tool_schemas(
-            node.tool_uuids
+            node.tool_uuids,
+            mcp_tool_filters=getattr(node, "mcp_tool_filters", None),
         )
         functions.extend(custom_tool_schemas)