feat(dict): make the build's dictionary version deploy-authoritative

The dictionary lives on a persistent volume seeded from the image once and never
re-seeded, so a redeploy that bumped BACKEND_DICT_VERSION left the new DAWGs
unreachable (the volume mount shadows the image copy) and the active version stuck
at whatever the admin console last installed — a native offline-first client then
fetched the server's older pinned version over the network instead of using its
bundled dict.

On boot the backend now DELIVERS the build version onto the volume add-only, from a
second unshadowed image copy at BACKEND_DICT_SEED_DIR, into DICT_DIR/<version>/ when
absent (the flat seed and prior uploads untouched, so in-flight games keep theirs),
and InitActiveVersion makes the build version active — except a console-installed
version NEWER than the build (compared numerically) is not downgraded by a restart.
The .seed_version guard still protects the flat seed's label (a bump is a new
subdirectory, never a relabel). The console stays for out-of-band updates.

Docs: ARCHITECTURE.md §5, deploy/README.md, seedmarker.go. Tests: engine.DeliverVersion
(add-only, idempotent, flat-seed skip), compareDictVersions, and the dictionary-update
integration test's deploy-delivers path.

backend/cmd/backend/main.go

@@ -111,6 +111,12 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	}
 	logger.Info("database migrations applied")
 
+	// Deliver the build's dictionary version onto the persistent volume if a redeploy
+	// bumped it (add-only; old versions in-flight games pin are untouched), so the new
+	// dictionary is resident and can be activated below without an admin upload.
+	if err := engine.DeliverVersion(cfg.Game.DictDir, cfg.Game.DictSeedDir, cfg.Game.DictVersion); err != nil {
+		return fmt.Errorf("deliver dictionary version: %w", err)
+	}
 	registry, err := engine.OpenWithVersions(cfg.Game.DictDir, cfg.Game.DictVersion)
 	if err != nil {
 		return fmt.Errorf("load dictionaries: %w", err)
@@ -118,6 +124,7 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	defer func() { _ = registry.Close() }()
 	logger.Info("dictionaries loaded",
 		zap.String("dir", cfg.Game.DictDir),
+		zap.String("seed_dir", cfg.Game.DictSeedDir),
 		zap.String("version", cfg.Game.DictVersion))
 
 	// Admin console: an optional backend client to the Telegram connector
@@ -147,10 +154,10 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	accounts := account.NewStore(db)
 	accounts.SetMetrics(tel.MeterProvider().Meter("scrabble/backend/account"))
 	games := game.NewService(game.NewStore(db), accounts, registry, cfg.Game, logger)
-	// Reconcile the persisted active dictionary version with the registry: a
-	// version activated through the admin console (and written to the dictionary
-	// volume) is adopted again after a restart; otherwise the configured seed
-	// version is kept and persisted (docs/ARCHITECTURE.md §5).
+	// Reconcile the active dictionary version with the registry: the build version
+	// (delivered above) becomes active so a redeploy that bumped it goes live for new
+	// games, except a newer version installed out-of-band through the admin console,
+	// which is not downgraded by a restart (docs/ARCHITECTURE.md §5).
 	if err := games.InitActiveVersion(ctx); err != nil {
 		return fmt.Errorf("init active dictionary version: %w", err)
 	}