feat(api): M4.2 — REST surface + pgx Postgres store + OpenAPI 3.1

Full M4.2 deliverable: 16 endpoints (tenants CRUD + lifecycle, catalog, entitlements, API keys with argon2 hashing, audit append + filter), Store interface with pgx-backed Postgres + in-memory parallel implementations exercised by the same eachStore harness, openapi.yaml at 3.1 with kin-openapi contract test. M4.3 adds auth.

Refs: M4.2

cmd/server/main.go

@@ -12,6 +12,7 @@ import (
 
 	"gitea.meghsakha.com/platform/tenant-registry/internal/config"
 	"gitea.meghsakha.com/platform/tenant-registry/internal/server"
+	"gitea.meghsakha.com/platform/tenant-registry/internal/store"
 )
 
 func main() {
@@ -24,10 +25,27 @@ func main() {
 		os.Exit(1)
 	}
 
-	mux := server.NewRouter(cfg, logger)
+	bootCtx, cancelBoot := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancelBoot()
+
+	var s store.Store
+	if cfg.DatabaseURL == "" {
+		slog.Warn("DATABASE_URL not set — running with in-memory store (dev only)")
+		s = store.NewMemory()
+	} else {
+		pg, err := store.NewPostgres(bootCtx, cfg.DatabaseURL)
+		if err != nil {
+			slog.Error("postgres connect failed", "err", err)
+			os.Exit(1)
+		}
+		s = pg
+	}
+	defer s.Close()
+
+	handler := server.NewRouter(&server.Server{Cfg: cfg, Log: logger, Store: s})
 	srv := &http.Server{
 		Addr:         cfg.Addr,
-		Handler:      mux,
+		Handler:      handler,
 		ReadTimeout:  10 * time.Second,
 		WriteTimeout: 30 * time.Second,
 		IdleTimeout:  60 * time.Second,
@@ -37,7 +55,7 @@ func main() {
 	defer stop()
 
 	go func() {
-		slog.Info("tenant-registry listening", "addr", cfg.Addr, "env", cfg.Env)
+		slog.Info("tenant-registry listening", "addr", cfg.Addr, "env", cfg.Env, "store", storeKind(s))
 		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
 			slog.Error("server crashed", "err", err)
 			os.Exit(1)
@@ -54,3 +72,14 @@ func main() {
 	}
 	slog.Info("bye")
 }
+
+func storeKind(s store.Store) string {
+	switch s.(type) {
+	case *store.Memory:
+		return "memory"
+	case *store.Postgres:
+		return "postgres"
+	default:
+		return "unknown"
+	}
+}