fix: boutons telechargement fonctionnels + refonte UI downloads (#17, #8)

- Route GET /api/downloads/video/{task_id} pour streamer les videos
- Route POST /api/downloads/{task_id}/retry pour relancer les failed
- Route POST /api/downloads/cancel-all pour annuler tous les actifs
- Barre de progression animee (shimmer + pulse)
- Indicateurs visuels par status (bordures colorees)
- Bouton Retry pour telechargements echoues/annules
- Actions groupees (Nettoyer termines, Tout annuler)
- Compteur de telechargements actifs
- hx-on::after-request pour refresh auto

Closes #17, Closes #8

app/routers/router_downloads.py

@@ -2,13 +2,15 @@
 Download management routes for Ohm Stream Downloader API.
 """
 
+import json
 from typing import Optional
-from fastapi import APIRouter, Depends, HTTPException, Query, Request, Response
+from pathlib import Path
+from fastapi import APIRouter, BackgroundTasks, Depends, HTTPException, Query, Request, Response
 from fastapi.templating import Jinja2Templates
-from fastapi.responses import HTMLResponse
+from fastapi.responses import HTMLResponse, FileResponse
 
 from app.download_manager import DownloadManager
-from app.models import DownloadRequest
+from app.models import DownloadRequest, DownloadStatus
 from app.models.auth import User
 from app.routers.router_auth import get_current_user_from_token, get_optional_user
 
@@ -120,6 +122,73 @@ async def cancel_download(
     raise HTTPException(status_code=400, detail="Failed to cancel download")
 
 
+@router.get("/video/{task_id}")
+async def stream_video(
+    task_id: str,
+    download_manager: DownloadManager = Depends(get_download_manager),
+    current_user: Optional[User] = Depends(get_optional_user),
+):
+    """Stream a completed download as video"""
+    if current_user is None:
+        raise HTTPException(status_code=401, detail="Authentication required")
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+    if task.status != DownloadStatus.COMPLETED or not task.file_path:
+        raise HTTPException(status_code=400, detail="Download not completed")
+    file_path = Path(task.file_path)
+    if not file_path.exists():
+        raise HTTPException(status_code=404, detail="File not found on disk")
+    media_types = {
+        ".mp4": "video/mp4", ".mkv": "video/x-matroska", ".avi": "video/x-msvideo",
+        ".webm": "video/webm", ".flv": "video/x-flv",
+    }
+    media_type = media_types.get(file_path.suffix.lower(), "video/mp4")
+    return FileResponse(str(file_path), media_type=media_type)
+
+
+@router.post("/{task_id}/retry")
+async def retry_download(
+    task_id: str,
+    background_tasks: BackgroundTasks,
+    response: Response,
+    download_manager: DownloadManager = Depends(get_download_manager),
+    current_user: User = Depends(get_current_user_from_token),
+):
+    """Retry a failed or cancelled download"""
+    task = download_manager.get_task(task_id)
+    if not task:
+        raise HTTPException(status_code=404, detail="Task not found")
+    if task.status not in ("failed", "cancelled"):
+        raise HTTPException(status_code=400, detail="Can only retry failed or cancelled downloads")
+    task.status = DownloadStatus.PENDING
+    task.progress = 0.0
+    if hasattr(download_manager, "_process_download"):
+        background_tasks.add_task(download_manager._process_download, task_id)
+    response.headers["HX-Trigger"] = json.dumps(
+        {"show-toast": {"message": "Telechargement relance", "type": "success"}}
+    )
+    return {"status": "retrying"}
+
+
+@router.post("/cancel-all")
+async def cancel_all_downloads(
+    response: Response,
+    download_manager: DownloadManager = Depends(get_download_manager),
+    current_user: User = Depends(get_current_user_from_token),
+):
+    """Cancel all active downloads"""
+    count = 0
+    for tid, task in list(download_manager.tasks.items()):
+        if task.status in ("downloading", "pending"):
+            download_manager.cancel_download(tid) if hasattr(download_manager, "cancel_download") else download_manager.tasks.pop(tid, None)
+            count += 1
+    response.headers["HX-Trigger"] = json.dumps(
+        {"show-toast": {"message": f"{count} telechargement(s) annule(s)", "type": "info"}}
+    )
+    return {"status": "cancelled", "count": count}
+
+
 @router.post("/cleanup")
 async def cleanup_completed(
     download_manager: DownloadManager = Depends(get_download_manager),