QONTO-WP-0003-T02: MCP tool catalog on the shared capability core

Add qonto_org_summary, qonto_list_transactions, and qonto_cost_run_rate_hints
MCP tools, all routed through CapabilityService with protocol="mcp" -- same
PolicyEngine.decide() path as REST, same deny-reason vocabulary. Skip
snapshot_bundle as an MCP tool (REST already covers the composite read; not
a separate privilege).

CapabilityService now threads protocol through _execute/_emit_audit instead
of hardcoding "rest". cost_run_rate_hints gets its own service method since
it's an independent policy capability, not only a snapshot sub-field.

Actor identity reuses REST's X-Actor-* header convention via a shared
auth.actor_claims_from_headers(), read from the MCP Context's request when
present. Fixed streamable_http_path defaulting to "/mcp", which doubled to
"/mcp/mcp" once mounted under the "/mcp" prefix.

Verified end-to-end with the mcp SDK's streamablehttp_client against the
live fixture-backed server: tool list, allow/deny paths, and X-Actor-ID
flowing through to the audit log exactly like REST.

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

src/qonto_assistant/app.py

@@ -40,7 +40,7 @@ def create_app(
         concurrency_limiter=concurrency_limiter,
     )
 
-    mcp_server = create_mcp_server(settings=settings)
+    mcp_server = create_mcp_server(settings=settings, service=service)
     mcp_app = mcp_server.streamable_http_app()
 
     @asynccontextmanager