Converter: cover real Ren'Py games better, add folder import and dry run

Checked against six real games (Ren'Py 7.5 and 8.x):
- nested labels and named menus become jump anchors inside label bodies
- call with arguments and labels with parameters (dynamically scoped)
- frame-by-frame ATL images, Movie frames, layeredimage, camera, Shake,
  custom audio channels via register_channel, show text with expressions
- generator expressions in Python, no SyntaxWarning noise from decompiled code

Also:
- app.import_dir converts an unpacked game folder without changing it
- app.converter.analyze dry-runs the script part of the converter
- imports use their own "importing" status so a worker restart can't hijack them

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/app/import_dir.py

@@ -0,0 +1,48 @@
+"""Import an already unpacked game from a folder on the server.
+
+    python -m app.import_dir /games/Some-Game [--title "Name"] [--owner admin]
+
+The folder is only read; the converted copy goes to the blob store like an upload.
+"""
+
+import argparse
+import asyncio
+from pathlib import Path
+
+from sqlalchemy import select
+
+from app.db import SessionLocal
+from app.models import Game, GameVersion, Role, User
+from app.worker import convert
+
+
+async def main() -> None:
+    ap = argparse.ArgumentParser()
+    ap.add_argument("path", type=Path)
+    ap.add_argument("--title")
+    ap.add_argument("--owner", help="username; defaults to the first admin")
+    args = ap.parse_args()
+    if not args.path.is_dir():
+        raise SystemExit(f"{args.path} is not a directory")
+
+    async with SessionLocal() as db:
+        stmt = select(User).join(Role).order_by(User.id)
+        stmt = stmt.where(User.username == args.owner) if args.owner else stmt.where(Role.name == "admin")
+        owner = await db.scalar(stmt.limit(1))
+        if owner is None:
+            raise SystemExit("owner not found")
+        game = Game(title=args.title or args.path.name, created_by_id=owner.id)
+        db.add(game)
+        await db.flush()
+        version = GameVersion(game_id=game.id, owner_id=owner.id, name="Оригинал",
+                              upload_name=args.path.name, status="importing")
+        db.add(version)
+        await db.commit()
+        game_id, version_id = game.id, version.id
+
+    ok = await convert(version_id, args.path, args.path.name)
+    print(f"game {game_id}, version {version_id}: {'ready' if ok else 'failed'}")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())