feat: in-process HTTP search; /get /stats /audit /ingest. (#13)

bin/brain/serve.go (ladybug tags) calls internal/brain instead of exec.
HTTP tests inject a fake API so CI stays cgo-free. ExecSearcher remains
the fallback when the binary is built without system_ladybug.

bin/brain/serve_exec.go

@@ -0,0 +1,20 @@
+//go:build brain_serve && !system_ladybug
+//
+// Fallback serve when ladybug cgo is not in the build (CI / tags=brain_serve).
+// Production shebang is serve.go (in-process).
+package main
+
+import (
+	"os"
+
+	"github.com/eSlider/2dph/internal/httpapi"
+)
+
+func main() {
+	if os.Getenv("KB_ROOT") == "" {
+		if wd, err := os.Getwd(); err == nil {
+			os.Setenv("KB_ROOT", wd)
+		}
+	}
+	httpapi.Run(nil)
+}