Add SQLite persistence, import-snapshot tool, and karma functionality

server/migrations/20260417173916_fix_deck_weapon.sql

@@ -0,0 +1,13 @@
+-- +goose Up
+
+-- Delete deck characters with empty weapons (always a bug).
+DELETE FROM user_deck_characters
+WHERE main_user_weapon_uuid = '';
+
+-- Delete decks that reference deleted deck characters.
+DELETE FROM user_decks
+WHERE user_deck_character_uuid01 NOT IN (SELECT user_deck_character_uuid FROM user_deck_characters)
+   AND user_deck_character_uuid01 != '';
+
+-- +goose Down
+-- No rollback needed: EnsureDefaultDeck recreates decks on next SetTutorialProgress call.