feat(lobby): F8-04b hierarchical sidebar + paid-tier gate for create-game

Reshape the lobby UI from a single Overview into a two-level sidebar
(games · profile · DEV synthetic-reports) with four games sub-panels
(active-past · recruitment · invitations · private-games). Move the
`create new game` button into the private-games panel, merge the
applications section into recruitment cards as status chips, and add
DEV-only synthetic-report loader as a top-level screen.

Add a paid-tier gate at backend `lobby.game.create`: free callers get
`403 forbidden` before the lobby service is invoked. The UI hides the
private-games sub-panel + create button on free tier (DEV affordances
flag overrides). Update every integration test that creates a game to
use a new `testenv.PromoteToPaid` helper; add a new
`TestLobbyFlow_FreeUserCreateGameForbidden`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/frontend/src/lib/screens/lobby-create-screen.svelte

@@ -40,6 +40,15 @@
 
 	function describeLobbyError(err: unknown): string {
 		if (err instanceof LobbyError) {
+			// Free-tier callers reach this branch when the backend gate
+			// at `lobby.game.create` rejects them. Show the dedicated
+			// inline message instead of the generic "operation
+			// forbidden" — the user got to this screen via the
+			// `private games` panel, so we want to spell out that the
+			// gate is the tier (not a permission misconfig).
+			if (err.code === "forbidden") {
+				return i18n.t("lobby.create.error.forbidden");
+			}
 			const key = `lobby.error.${err.code}` as TranslationKey;
 			const translated = i18n.t(key);
 			if (translated !== key) {
@@ -93,7 +102,10 @@
 				turnSchedule: trimmedSchedule,
 				targetEngineVersion: targetEngineVersion.trim() || DEFAULT_TARGET_ENGINE_VERSION,
 			});
-			appScreen.go("lobby");
+			// Land on the private-games panel where the freshly created
+			// game shows up — the lobby-data store will refresh on next
+			// mount.
+			appScreen.go("games-private-games");
 		} catch (err) {
 			formError = describeLobbyError(err);
 		} finally {