test: enforce response-schema map covers every route

[ethanj]

Summary

Follow-up to #37. Codex flagged that the runtime validator silently skips unmapped routes, so a future route addition or path rename could drop response validation for that endpoint without anyone noticing — the router-level middleware still looks protected.

This closes the maintenance gap with four assertions that walk both createMemoryRouter and createAgentRouter's Express stacks and cross-check against the schema map:

• Every memory route has a MEMORY_RESPONSE_SCHEMAS entry.
• Every agent route has an AGENT_RESPONSE_SCHEMAS entry.
• No MEMORY_RESPONSE_SCHEMAS key points at a non-existent route (catches stale entries left behind when a route is deleted).
• No AGENT_RESPONSE_SCHEMAS key points at a non-existent route.

Uses stub MemoryService / AgentTrustRepository instances — Express route registration doesn't invoke service methods, so the stack is fully populated without a live DB. Test runs in ~4ms.

Follow-up

Codex's stronger suggestion — deriving the map from the same registration source that builds the OpenAPI spec — would make the gap structurally impossible instead of catching it in CI. That's a larger restructure (typed registerRoute(method, path, { requestBody, responseSchema, handler }) helper used by both openapi.ts and the router). Noted as a separate refactor; this test is the minimum bar.

Test plan

• Four new assertions pass
• All 1041 core tests pass (1037 + 4 new)
• CI green end-to-end