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.

internal/httpapi/spec.go

@@ -1,5 +1,7 @@
 package httpapi
 
+import "strings"
+
 // Shared HTTP surface: OpenAPI paths and MCP tools are generated from Ops.
 // ServeHTTP must keep the same path strings.
 
@@ -124,3 +126,19 @@ func MCPTools() []MCPTool {
 	}
 	return out
 }
+
+// SkillMarkdown is the Cursor skill fragment generated from Ops/MCPTools.
+func SkillMarkdown() string {
+	var b strings.Builder
+	b.WriteString("# brain HTTP / MCP tools\n\n")
+	b.WriteString("Generated from `internal/httpapi.Ops`. Do not edit by hand.\n\n")
+	b.WriteString("Serve: `bin/brain/serve.go` (`GET /openapi.json`, `POST /mcp`).\n\n")
+	for _, t := range MCPTools() {
+		b.WriteString("- `")
+		b.WriteString(t.Name)
+		b.WriteString("` — ")
+		b.WriteString(t.Description)
+		b.WriteString("\n")
+	}
+	return b.String()
+}

internal/httpapi/spec_test.go

@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -76,6 +78,17 @@ func TestMCPToolsListAndCall(t *testing.T) {
 	}
 }
 
+func TestSkillMarkdownMatchesCommittedFile(t *testing.T) {
+	want, err := os.ReadFile(filepath.Join("..", "..", "skills", "brain", "tools.md"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := SkillMarkdown()
+	if got != string(want) {
+		t.Fatalf("skills/brain/tools.md stale; regenerate from SkillMarkdown()\n--- got ---\n%s\n--- want ---\n%s", got, want)
+	}
+}
+
 func postJSON(t *testing.T, h http.Handler, path, raw string) (int, []byte) {
 	t.Helper()
 	req := httptest.NewRequest(http.MethodPost, path, strings.NewReader(raw))