feat: mount MCP server, add bearer auth, and guard outbound calls

The MCP server was created but never mounted — no client could reach
it. Mount it at /mcp/ over streamable HTTP with a combined lifespan,
resolving the gateway lazily so mounting happens at app construction.

Security and safety for the agent surface:
- One static API_TOKEN (SecretStr) enforced across REST (dependency),
  WebSocket (query param/header before accept), and MCP
  (StaticTokenVerifier). Startup refuses tokenless non-loopback binds.
- Emergency numbers (911/9911/112) always refused on make_call, plus a
  MAX_CONCURRENT_CALLS cap; ValueError surfaces as 400/ToolError.
- Safe defaults: debug off, no credential in default DATABASE_URL,
  SIP/LLM/TTS secrets as SecretStr.

Cleanups:
- Delete broken learn_call_flow tool (wrong ctor args, nonexistent
  method) and the never-fed CallAnalytics service; keep
  call_flow_learner for proper wiring later.
- Trim dial_plan to what is actually used (emergency guard, extension
  allocation); delete the unreferenced matcher/normaliser.
- Register call_history before calls so /api/calls/history is no
  longer shadowed by /api/calls/{call_id}.
- fastmcp pinned >=3.0 (http_app + StaticTokenVerifier).

New tests: MCP in-memory client (tool surface, lazy gateway, emergency
refusal, call cap) and API security (401 paths, route order, mount).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

api/calls.py

@@ -46,6 +46,8 @@ async def make_call(
             number=request.number,
             mode=request.mode.value,
         )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
         raise HTTPException(status_code=500, detail=str(e))
 
@@ -86,6 +88,8 @@ async def hold_slayer(
             mode="hold_slayer",
             message="Hold Slayer activated. I'll ring you when a human picks up. ☕",
         )
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
         raise HTTPException(status_code=500, detail=str(e))