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/internal/game/service.go

@@ -232,21 +232,31 @@ func (svc *Service) ActiveVersion() string {
 }
 
 // InitActiveVersion reconciles the persisted active dictionary version with the
-// registry at startup. If a version was persisted and is resident, it becomes the
-// active version; otherwise the configured seed version is kept and persisted as
-// the initial active version. Call once during wiring, before serving traffic.
+// registry at startup and makes the build's version (BACKEND_DICT_VERSION, delivered
+// resident by engine.DeliverVersion) authoritative: a redeploy that bumped the build
+// version thus activates it for new games without any admin step, while old games keep
+// the version they pin. The one exception is a version installed out-of-band through
+// the admin console that is NEWER than the build version and still resident — it is
+// kept, so a restart on an older image never downgrades a hotfix. A build version that
+// is not resident (delivery disabled or a partial state) falls back to a resident
+// persisted version. The chosen version is persisted so the admin console reflects it.
+// Call once during wiring, before serving traffic.
 func (svc *Service) InitActiveVersion(ctx context.Context) error {
 	persisted, ok, err := svc.store.GetActiveDictVersion(ctx)
 	if err != nil {
 		return err
 	}
-	if ok && svc.versionResident(persisted) {
-		svc.verMu.Lock()
-		svc.version = persisted
-		svc.verMu.Unlock()
-		return nil
+	target := svc.activeVersion() // the build seed version (config.DictVersion)
+	if ok && svc.versionResident(persisted) && compareDictVersions(persisted, target) > 0 {
+		target = persisted // a newer out-of-band install wins over the build version
 	}
-	return svc.store.SetActiveDictVersion(ctx, svc.activeVersion())
+	if !svc.versionResident(target) && ok && svc.versionResident(persisted) {
+		target = persisted // the build version is unloadable — keep a resident one
+	}
+	svc.verMu.Lock()
+	svc.version = target
+	svc.verMu.Unlock()
+	return svc.store.SetActiveDictVersion(ctx, target)
 }
 
 // SetActiveVersion records version as the active dictionary version, persisting it