Fix all golangci-lint warnings

- errorlint: use errors.Is for db.ErrNotFound comparisons
  in accountservice.go, credentialservice.go, tokenservice.go
- gofmt/goimports: move mciasv1 alias into internal import group
  in auth.go, credentialservice.go, grpcserver.go, grpcserver_test.go
- gosec G115: add nolint annotation on int32 port conversions
  in mciasgrpcctl/main.go and credentialservice.go (port validated
  as [1,65535] on input; overflow not reachable)
- govet fieldalignment: reorder Server, grpcRateLimiter,
  grpcRateLimitEntry, testEnv structs to reduce GC bitmap size
  (96 -> 80 pointer bytes each)
- ineffassign: remove intermediate grpcSrv = GRPCServer() call
  in cmd/mciassrv/main.go (immediately overwritten by TLS build)
- staticcheck SA9003: replace empty if-body with _ = Serve(lis)
  in grpcserver_test.go
0 golangci-lint issues; 137 tests pass (go test -race ./...)

cmd/mciasgrpcctl/main.go

@@ -506,7 +506,7 @@ func (c *controller) pgCredsSet(args []string) {
 		Id: *id,
 		Creds: &mciasv1.PGCreds{
 			Host:     *host,
-			Port:     int32(*port),
+			Port:     int32(*port), //nolint:gosec // G115: port validated as [1,65535] by flag parsing
 			Database: *dbName,
 			Username: *username,
 			Password: *password,