feat: declare OpenAPI response schemas for every route

[ethanj]

Summary

Every /v1 route in the OpenAPI spec now carries a concrete response schema instead of the permissive z.object({}).passthrough() placeholder that shipped before. npm run check:openapi (CI step) will now catch wire-shape drift between the formatters and the committed spec — the guardrail missing from the snake_case wire flip in #32.

What's in the PR

• src/schemas/responses.ts (new, ~400 lines) — Zod schemas mirroring every response shape emitted by src/routes/memory-response-formatters.ts and the inline route literals:
  • Top-level: Ingest, Search, Expand, List, GetMemory, Stats, Health, ConfigUpdate, Consolidate (scan∪execute discriminated union), Decay, Cap, LessonsList, LessonStats, LessonReport, Reconciliation, ReconcileStatus, ResetSource, Success, MutationSummary, AuditRecent, AuditTrail, Trust, ConflictsList, ResolveConflict, AutoResolveConflicts
  • Sub-schemas for nested wire shapes: Scope, MemoryRow, SearchMemoryItem, TierAssignment, LessonCheck, Consensus, RetrievalTrace / PackagingTrace / AssemblyTrace / Observability, ClusterCandidate, DecayCandidate, LessonRow, ClaimVersionRow, MemoryConflictRow, HealthConfig, AuditTrailEntry. These stay non-exported — they only compose the top-level exports.
• src/schemas/openapi.ts — every ok('...', GenericObjectResponse) replaced with its specific schema import. Error envelopes (400/404/410/500) unchanged.
• openapi.yaml + openapi.json regenerated deterministically — +3788 lines now document real response bodies.

Follow-up worth tracking

The route handlers don't yet parse their response through these schemas before sending (runtime drift detection). The spec-level check catches intentional formatter changes that forget to update schemas; runtime parsing would catch accidental Record<unknown> leaks but adds per-request cost. Noted as a follow-up.

Test plan

• npx tsc --noEmit clean
• All 1037 core tests pass
• npm run generate:openapi produces zero diff after regen
• npm run check:openapi passes locally
• Pre-commit fallow audit passes (4 changed files, 0 issues)
• CI green end-to-end