Add viewer database import and clarify backup actions.

Pairs export with validated .db restore, documents the difference from game
save imports, and renames the JSON upload button to Import game backup.

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

static/locales/en.json

@@ -21,8 +21,9 @@
     "langDe": "Deutsch"
   },
   "actions": {
-    "importBackup": "Import backup",
+    "importBackup": "Import game backup",
     "exportViewer": "Export viewer",
+    "importViewer": "Import viewer",
     "compare": "Compare",
     "dismiss": "Dismiss"
   },
@@ -224,6 +225,16 @@
     "copied": "Copied!",
     "copyPrompt": "Copy your viewer link:"
   },
+  "viewerDb": {
+    "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).",
+    "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).",
+    "importFailed": "Could not import viewer database",
+    "invalidFile": "Please select a .db file (viewer export)."
+  },
   "goals": {
     "filterAll": "All",
     "filterOpen": "Open",