feat: generate brain tools skill from OpenAPI; rename db-yaml to postgres (#21)

Cursor skills stay in lockstep with serve handlers. CI checks every bin/
path named in SKILL.md exists.

skills/brain/SKILL.md

@@ -45,5 +45,6 @@ are not wired yet); do not treat it as a graph walk.
 - If recall looks wrong, run `bin/brain/eval.go`; it gates control questions and
   should stay at or above 95% recall@5.
 - Agents: `GET /openapi.json` and `POST /mcp` on `bin/brain/serve.go` (same
-  handlers; tool names match paths `search`/`get`/`stats`/`audit`).
+  handlers; tool names match paths `search`/`get`/`stats`/`audit`). Generated
+  list: [tools.md](tools.md).
 - Never report an unconfirmed single-source local answer as fact.

skills/brain/tools.md

@@ -0,0 +1,11 @@
+# brain HTTP / MCP tools
+
+Generated from `internal/httpapi.Ops`. Do not edit by hand.
+
+Serve: `bin/brain/serve.go` (`GET /openapi.json`, `POST /mcp`).
+
+- `search` — deduction search (facts → info → web)
+- `get` — read one leaf by id
+- `stats` — index health
+- `audit` — facts confidence histogram
+- `ingest` — rebuild hint (write is v2)