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>

test_db_goals.py

@@ -20,6 +20,7 @@ from db import (
     skill_timeline,
     summarize_import_changes,
 )
+from viewers import inspect_viewer_db, restore_viewer_db
 
 
 def _minimal_save(coins: int = 100, level: int = 5) -> dict:
@@ -78,6 +79,13 @@ def test_relative_and_skill_goals() -> None:
         changes = summarize_import_changes(snaps, db_path=db)
         assert changes["has_previous"] is False
 
+        db2 = Path(td) / "restored.db"
+        stats = restore_viewer_db(db, db2)
+        assert stats["snapshots"] >= 1
+        assert stats["goals"] == 2
+        inspected = inspect_viewer_db(db2)
+        assert inspected["goal_groups"] == 1
+
         print("all tests passed")