feat: OpenAPI and MCP from the same serve handlers (#20)

Agents get GET /openapi.json and POST /mcp. Tool names match
search/get/stats/audit paths so PicoClaw does not need shebangs.

docs/design.md

@@ -69,4 +69,11 @@ Conflicting pairings (≥2 yes vs ≥2 no) = hypothesis (OQ1 → v2 resolution).
 (`system_ladybug`). They do not exec Python. Control questions for recall@5
 live in `internal/brain/rank` so CI can test the table without libladybug.
 Python `bin/kb/{get,stats,eval}` remain for GitHub Actions until the runner
-has ladybug cgo. Index/write is still `bin/kb/index`.
+has ladybug cgo. Index/write is still `bin/kb/index`.
+
+## Agent API (D20)
+
+`bin/brain/serve.go` exposes the same `internal/httpapi.Ops` table as OpenAPI
+(`GET /openapi.json`) and MCP (`POST /mcp` JSON-RPC `tools/list` +
+`tools/call`). Tool names match paths: `search`, `get`, `stats`, `audit`.
+Agents should use these endpoints instead of shebang CLIs.