feat(admin): online dictionary update — upload archive, preview word diff, install & activate

Replace the dictionary hot-reload with an online update flow in the GM console
(/_gm/dictionary): the operator uploads scrabble-dawg-vX.Y.Z.tar.gz, previews the
per-variant words added/removed against the active dictionary, and confirms to
install + activate it. Versions are immutable; in-progress games keep their pinned
version while new games use the new one.

- engine: DiffWords (enumerate both DAWGs, decode only the differences), OpenFinder,
  Registry.Finder, DictFiles; OpenWithVersions skips the .staging area.
- dictadmin: hardened release-archive validation + extraction (path-traversal,
  symlink, oversize, entry-count rejection) and staging -> install (atomic rename).
- game: active dictionary version persisted in the dictionary_state singleton
  (single source of truth, restored on boot), concurrency-safe accessor.
- storage: BACKEND_DICT_DIR is a named volume seeded from the image (nonroot-owned),
  so uploaded versions persist across redeploys; the build's DICT_VERSION labels the
  seed and equals the resident tag (BACKEND_DICT_VERSION).
- docs: ARCHITECTURE §5, FUNCTIONAL (+ru), backend README, TESTING, PRERELEASE.

Tests: engine + dictadmin unit; integration upload->preview->install->activate->
restart->pin->immutability->CSRF.

backend/internal/adminconsole/views.go

@@ -43,7 +43,10 @@ type DashboardView struct {
 	ActiveGames    int
 	OpenComplaints int
 	PendingChanges int
-	Variants       []VariantVersions
+	// ActiveVersion is the dictionary version new games pin (the persisted active
+	// version), distinct from the per-variant resident versions.
+	ActiveVersion string
+	Variants      []VariantVersions
 }
 
 // UsersView is the paginated account list.
@@ -237,11 +240,13 @@ type ComplaintDetailView struct {
 	Resolved       bool
 }
 
-// DictionaryView lists the resident versions per variant and the pending
-// wordlist changes from accepted complaints.
+// DictionaryView lists the resident versions per variant, the active version new
+// games pin, and the pending wordlist changes from accepted complaints.
 type DictionaryView struct {
-	Variants []VariantVersions
-	Changes  []DictChangeRow
+	// ActiveVersion is the dictionary version new games pin; the update form sets it.
+	ActiveVersion string
+	Variants      []VariantVersions
+	Changes       []DictChangeRow
 }
 
 // DictChangeRow is one pending wordlist edit.
@@ -252,6 +257,32 @@ type DictChangeRow struct {
 	ResolvedAt string
 }
 
+// DictionaryPreviewView is the second step of a dictionary update: the version
+// parsed from the uploaded archive (editable before confirming), the staging token
+// that names the uploaded files on disk, the active version the diff is against, and
+// the per-variant word diff.
+type DictionaryPreviewView struct {
+	Version       string
+	Token         string
+	ActiveVersion string
+	Variants      []VariantDiffRow
+}
+
+// VariantDiffRow summarises one variant's word diff in the update preview.
+// AddedCount/RemovedCount are the full totals; AddedSample/RemovedSample are the
+// first words shown (capped); AddedTruncated/RemovedTruncated mark a capped list;
+// LargeRemoval flags a removal large enough to warrant caution before confirming.
+type VariantDiffRow struct {
+	Variant          string
+	AddedCount       int
+	RemovedCount     int
+	AddedSample      []string
+	RemovedSample    []string
+	AddedTruncated   bool
+	RemovedTruncated bool
+	LargeRemoval     bool
+}
+
 // BroadcastView is the operator-broadcast form page.
 type BroadcastView struct {
 	ConnectorEnabled bool