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>

frontend/src/pages/GamePage.tsx

@@ -7,6 +7,7 @@ const STATUS: Record<Version["status"], string> = {
   uploading: "загружается",
   queued: "в очереди",
   converting: "конвертируется",
+  importing: "импортируется",
   ready: "готова",
   failed: "ошибка",
 };
@@ -32,7 +33,7 @@ export function GamePage() {
   }, [load]);
 
   // poll while something is being converted
-  const busy = game?.versions.some((v) => ["uploading", "queued", "converting"].includes(v.status));
+  const busy = game?.versions.some((v) => ["uploading", "queued", "converting", "importing"].includes(v.status));
   useEffect(() => {
     if (!busy) return;
     const t = setInterval(() => void load(), 2000);
@@ -154,7 +155,7 @@ function VersionRow(props: {
           {v.status === "ready" && props.canFork && <button onClick={props.onFork}>Форк</button>}
           {(v.status === "ready" || v.status === "failed") && <button onClick={() => void toggleReport()}>Отчёт</button>}
           {v.status === "failed" && props.canManage && <button onClick={props.onRetry}>Повторить</button>}
-          {props.canManage && v.status !== "converting" && <button className="danger" onClick={props.onDelete}>Удалить</button>}
+          {props.canManage && !["converting", "importing"].includes(v.status) && <button className="danger" onClick={props.onDelete}>Удалить</button>}
         </div>
       </div>
       {report !== undefined && <Report report={report} />}