chore: remove legacy tables and series table scripts

- Removed mongoose dependency from package-lock.json.
- Deleted legacy import tables: ImportCandidateChapter, AssetNovelMapping, ImportJob, ImportSession, SourceAsset via new script `drop_legacy_import_tables.py`.
- Added script `drop_series_table.py` to drop the Series table.

Co-authored-by: Copilot <copilot@github.com>

scripts/drop_legacy_import_tables.py

@@ -0,0 +1,35 @@
+import os
+from urllib.parse import parse_qsl, urlencode, urlsplit, urlunsplit
+
+from dotenv import load_dotenv
+from sqlalchemy import create_engine, text
+
+
+def main() -> None:
+    load_dotenv()
+    database_url = os.getenv("DATABASE_URL")
+    if not database_url:
+        raise RuntimeError("DATABASE_URL missing")
+
+    parts = urlsplit(database_url)
+    filtered_query = [(k, v) for (k, v) in parse_qsl(parts.query, keep_blank_values=True) if k.lower() != "schema"]
+    normalized_url = urlunsplit((parts.scheme, parts.netloc, parts.path, urlencode(filtered_query), parts.fragment))
+
+    engine = create_engine(normalized_url)
+    tables = [
+        "ImportCandidateChapter",
+        "AssetNovelMapping",
+        "ImportJob",
+        "ImportSession",
+        "SourceAsset",
+    ]
+
+    with engine.begin() as conn:
+        for table in tables:
+            conn.execute(text(f'DROP TABLE IF EXISTS "{table}" CASCADE'))
+
+    print("Dropped legacy tables")
+
+
+if __name__ == "__main__":
+    main()