Migrate db, auth to mcdsl; remove mcias client dependency

- db.Open: delegate to mcdsl/db.Open
- db.Migrate: convert to mcdsl/db.Migration format, delegate
- auth: type aliases for TokenInfo/Authenticator/Config from mcdsl,
  re-export error sentinels, Logout helper
- cmd/server: construct auth.Authenticator from Config (not mcias.Client)
- server/routes.go logout: use auth.Logout(authenticator, token)
- grpcserver/auth.go: same logout pattern, fix Login return type
  (time.Time not string)
- webserver: replace mcias.Client with mcdsl/auth for service token
  validation; resolveUser degrades to raw UUID (TODO: restore when
  mcias client library is properly tagged)
- Dockerfiles: bump to golang:1.25-alpine, remove gcc/musl-dev,
  add VERSION build arg
- Deploy: add docker-compose-rift.yml with localhost-only port mapping
- Remove git.wntrmute.dev/kyle/mcias/clients/go dependency entirely
- All tests pass, net -185 lines

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/server/server_test.go

@@ -39,9 +39,8 @@ func setupTestServer(t *testing.T) (*Server, *seal.Manager, chi.Router) {
 	sealMgr := seal.NewManager(database, b, nil, slog.Default())
 	_ = sealMgr.CheckInitialized()
 
-	// Auth requires MCIAS client which we can't create in tests easily,
-	// so we pass nil and avoid auth-dependent routes in these tests.
-	authenticator := auth.NewAuthenticator(nil, slog.Default())
+	// Auth not exercised in these tests — token info is injected directly.
+	authenticator, _ := auth.NewAuthenticator(auth.Config{ServerURL: "http://localhost:0"}, slog.Default())
 	policyEngine := policy.NewEngine(b)
 	engineRegistry := engine.NewRegistry(b, slog.Default())