refactor: migrate main.py to modular routers and add project roadmap

- Migrated monolithic main.py to feature-scoped routers in app/routers/
- Added GEMINI.md for project context and AI instructional guidelines
- Updated README.md with a comprehensive modernization plan (SQL migration, robust scraping DSL, frontend modernization)
- Improved authentication with cookie support and modular JS
- Updated test suite and documentation

app/routers/router_downloads.py

@@ -0,0 +1,151 @@
+"""
+Download management routes for Ohm Stream Downloader API.
+"""
+
+import os
+
+from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException
+from fastapi.responses import FileResponse
+
+from app.download_manager import DownloadManager
+from app.models import DownloadRequest, DownloadStatus
+from app.utils import is_safe_filename, sanitize_filename
+
+router = APIRouter(prefix="/api/download", tags=["downloads"])
+
+
+def get_download_manager() -> DownloadManager:
+    from main import download_manager
+
+    return download_manager
+
+
+@router.post("")
+async def create_download(
+    request: DownloadRequest,
+    background_tasks: BackgroundTasks,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Create a new download task"""
+    if request.filename:
+        request.filename = sanitize_filename(request.filename)
+        if not is_safe_filename(request.filename):
+            raise HTTPException(
+                status_code=400,
+                detail="Invalid filename. Path traversal attempts are not allowed.",
+            )
+
+    task = download_manager.create_task(request)
+    background_tasks.add_task(download_manager.start_download, task.id)
+    return {"task_id": task.id, "task": task}
+
+
+@router.get("/direct")
+async def direct_download(
+    url: str,
+    filename: str,
+    background_tasks: BackgroundTasks,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Download directly from a video URL with custom filename"""
+    request = DownloadRequest(url=url, filename=filename)
+    task = download_manager.create_task(request)
+    background_tasks.add_task(download_manager.start_download, task.id)
+    return {"task_id": task.id, "task": task}
+
+
+@router.get("/{task_id}")
+async def get_download_status(
+    task_id: str,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Get status of a specific download"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+    return task
+
+
+@router.post("/{task_id}/pause")
+async def pause_download(
+    task_id: str,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Pause a download"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+    await download_manager.pause_download(task_id)
+    return {"status": "paused"}
+
+
+@router.post("/{task_id}/resume")
+async def resume_download(
+    task_id: str,
+    background_tasks: BackgroundTasks,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Resume a paused download"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+
+    if task.status == DownloadStatus.PAUSED:
+        background_tasks.add_task(download_manager.start_download, task_id)
+        return {"status": "resumed"}
+
+    return {"status": "already running or completed"}
+
+
+@router.delete("/{task_id}")
+async def delete_download(
+    task_id: str,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Delete/cancel a download"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+    await download_manager.delete_task(task_id)
+    return {"status": "deleted"}
+
+
+@router.get("/{task_id}/file")
+async def download_file(
+    task_id: str,
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """Download the completed file"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+
+    if task.status != DownloadStatus.COMPLETED:
+        raise HTTPException(status_code=400, detail="Download not completed")
+
+    if not task.file_path or not os.path.exists(task.file_path):
+        raise HTTPException(status_code=404, detail="File not found")
+
+    return FileResponse(
+        task.file_path, filename=task.filename, media_type="application/octet-stream"
+    )
+
+
+@router.get("/")
+async def list_downloads(
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """List all download tasks"""
+    return {"downloads": download_manager.get_all_tasks()}
+
+
+# Legacy endpoint for /api/downloads
+legacy_router = APIRouter(prefix="/api", tags=["downloads-legacy"])
+
+
+@legacy_router.get("/downloads")
+async def list_all_downloads(
+    download_manager: DownloadManager = Depends(get_download_manager),
+):
+    """List all download tasks (legacy endpoint at /api/downloads)"""
+    return {"downloads": download_manager.get_all_tasks()}