QONTO-WP-0003-T03: MCP client auth + shared multi-harness config snippet

Gate /mcp with a shared-secret bearer token (QONTO_ASSISTANT_MCP_TOKEN,
mcp_auth.py::BearerTokenAuthMiddleware, constant-time compare, REST
untouched) since no OIDC issuer exists in this fleet yet -- pointing
FastMCP's OAuth Protected Resource flow at a non-existent issuer would be
worse than not having it. This token is a service credential, never a bank
credential; per-actor identity stays the existing X-Actor-* convention.

Add docs/mcp-integration.md: tool catalog, the two-layer auth model (workload
auth today vs. deferred OIDC target), and one shared {"mcpServers": {...}}
client config snippet (url + headers) usable across Claude Code, Claude
Desktop, Cursor, and Codex/Grok-style harnesses.

Verified live using only that snippet: unauthenticated and wrong-token
requests get 401 before reaching any tool; a request built from the
snippet's URL + headers lists tools and calls qonto_org_summary
successfully against the fixture-backed server.

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

docs/operator-runbook.md

@@ -162,6 +162,13 @@ PY
 Use `window_days=31` for a recent-activity view. Use `window_days=90` or `93`
 when recurring fixed-cost hints are required.
 
+## MCP surface
+
+Phase 2 mounts a streamable-HTTP MCP adapter at `/mcp` on this same process,
+sharing the policy kernel and audit layer above. See
+`docs/mcp-integration.md` for the tool catalog, the auth model
+(`QONTO_ASSISTANT_MCP_TOKEN`), and the shared client config snippet.
+
 ## CostRunRate refresh path
 
 `binky-control` should consume `GET /v1/snapshot` and extract: