Move viewer export/import into a dedicated Backup tab.

Keeps game save import in the sidebar while grouping viewer database
backup actions with their explanation in the main navigation.

Co-authored-by: Cursor <cursoragent@cursor.com>

static/locales/en.json

@@ -12,7 +12,8 @@
     "equipment": "Equipment",
     "quests": "Quests",
     "combat": "Combat",
-    "history": "History"
+    "history": "History",
+    "backup": "Backup"
   },
   "settings": {
     "language": "Language",
@@ -229,6 +230,7 @@
     "title": "Viewer backup",
     "helpTitle": "What is this?",
     "helpBody": "The viewer stores imported game backups, history charts, and goals in a SQLite database on the server. Export downloads that database as a backup. Import restores it and replaces all current viewer data. This is not the same as importing a game save (.json).",
+    "gameBackupNote": "To add a new game save snapshot, use Import game backup in the sidebar.",
     "exportHint": "Download the SQLite database with all snapshots, history, and goals",
     "importConfirm": "All current viewer data (snapshots, history, goals) will be replaced by the imported .db file. Continue?",
     "importSuccess": "Viewer restored: {snapshots} snapshot(s), {goals} goal(s).",