feat(admin-console): Stage 4 — games & runtimes domain

Add the games, runtime, and engine-version pages over the existing lobby,
runtime, and engine-version services (no new business logic).

- GET/POST /_gm/games                         list + create public game
- GET      /_gm/games/{id}                    detail incl. runtime snapshot
- POST     /_gm/games/{id}/force-start|stop    game state actions
- POST     /_gm/games/{id}/ban-member          ban a member (uuid + reason)
- POST     /_gm/games/{id}/runtime/restart|patch|force-next-turn
- GET/POST /_gm/engine-versions               registry + register
- POST     /_gm/engine-versions/{ver}/disable disable a version

Console depends on GameAdmin / RuntimeAdmin / EngineVersionAdmin interfaces
(satisfied by the concrete services) so the pages render in tests without a
database. Collection-mutating POSTs are mounted on the collection path to avoid
a static-vs-param route conflict in gin. Writes flow through the CSRF guard and
redirect back; the create form parses datetime-local as UTC.

Tests: list/detail (with and without a runtime), create (visibility/owner/time
assertions), force-start (+ bad-CSRF), ban-member (+ bad uuid), runtime patch
(+ missing version), engine-version list/register/disable, and unavailable.

Docs: backend/docs/admin-console.md page inventory extended.

backend/internal/adminconsole/games.go

@@ -0,0 +1,67 @@
+package adminconsole
+
+// GameRow is one line in the games list table.
+type GameRow struct {
+	GameID       string
+	GameName     string
+	Visibility   string
+	Status       string
+	Owner        string
+	Players      string
+	TurnSchedule string
+	CreatedAt    string
+}
+
+// GamesListData is the view model for the paginated games list.
+type GamesListData struct {
+	Items    []GameRow
+	Page     int
+	PageSize int
+	Total    int
+	HasPrev  bool
+	HasNext  bool
+	PrevPage int
+	NextPage int
+}
+
+// GameDetailData is the view model for a single game, combining the lobby
+// record with the runtime snapshot and the available actions.
+type GameDetailData struct {
+	GameID              string
+	GameName            string
+	Description         string
+	Visibility          string
+	Status              string
+	Owner               string
+	MinPlayers          int32
+	MaxPlayers          int32
+	StartGapHours       int32
+	StartGapPlayers     int32
+	TurnSchedule        string
+	TargetEngineVersion string
+	EnrollmentEndsAt    string
+	CreatedAt           string
+	StartedAt           string
+	FinishedAt          string
+
+	HasRuntime           bool
+	RuntimeStatus        string
+	CurrentEngineVersion string
+	EngineHealth         string
+	CurrentTurn          int32
+	NextGenerationAt     string
+	Paused               bool
+}
+
+// EngineVersionRow is one line in the engine-version registry table.
+type EngineVersionRow struct {
+	Version   string
+	ImageRef  string
+	Enabled   bool
+	CreatedAt string
+}
+
+// EngineVersionsData is the view model for the engine-version registry page.
+type EngineVersionsData struct {
+	Items []EngineVersionRow
+}