feat(PROJ-13): OpenAPI 3.0 Spec + GET /api/v1/docs Endpoint

Serves the static OpenAPI YAML via go:embed. Completes the last
open acceptance criterion for PROJ-13. PROJ-44 marked Deployed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/v1_docs_handler.go

@@ -0,0 +1,17 @@
+package api
+
+import (
+	_ "embed"
+	"net/http"
+)
+
+//go:embed openapi.yaml
+var openapiSpec []byte
+
+// handleV1Docs serves the OpenAPI 3.0 spec for the external REST API.
+// GET /api/v1/docs
+func (s *Server) handleV1Docs(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/yaml; charset=utf-8")
+	w.WriteHeader(http.StatusOK)
+	w.Write(openapiSpec)
+}