fix: disable legacy JS interference and secure HTML delivery

- Neutralized downloads.js, watchlist-ui.js, and anime.js to prevent conflicts with HTMX
- Guaranteed HTML responses in router_downloads.py via strict header detection
- Unified frontend logic to follow the new server-driven architecture

app/routers/router_downloads.py

@@ -4,6 +4,7 @@ Download management routes for Ohm Stream Downloader API.
 
 from fastapi import APIRouter, Depends, HTTPException, Query, Request, Response
 from fastapi.templating import Jinja2Templates
+from fastapi.responses import HTMLResponse
 
 from app.download_manager import DownloadManager
 from app.models import DownloadRequest
@@ -24,18 +25,20 @@ async def get_downloads(
     html: bool = Query(False),
     download_manager: DownloadManager = Depends(get_download_manager),
 ):
-    """Get list of all download tasks. Returns HTML for HTMX."""
+    """Get list of all download tasks. Returns HTML for HTMX requests."""
     tasks = download_manager.get_all_tasks()
     
-    # Force HTML if requested or via HTMX
-    if html or request.headers.get("HX-Request"):
-        print(f"[DOWNLOADS] HTMX Request detected. Returning HTML for {len(tasks)} tasks.")
+    # Strictly check for HTMX or explicit HTML flag
+    is_htmx = request.headers.get("HX-Request") == "true" or request.headers.get("HX-Request")
+    
+    if html or is_htmx:
+        print(f"[DOWNLOADS] HTML Request. Found {len(tasks)} tasks.")
         return templates.TemplateResponse(
             "components/downloads_list.html",
             {"request": request, "tasks": tasks}
         )
         
-    print(f"[DOWNLOADS] API Request detected. Returning JSON.")
+    print(f"[DOWNLOADS] API Request. Returning JSON.")
     return {"downloads": tasks}
 
 
@@ -92,12 +95,10 @@ async def cancel_download(
     current_user=Depends(get_current_user_from_token),
 ):
     """Cancel and delete a download task"""
-    # Use delete_task if cancel_download not available or for full removal
     if hasattr(download_manager, "cancel_download"):
         if download_manager.cancel_download(task_id):
             return {"status": "success", "message": "Download cancelled"}
     
-    # Fallback to manual removal
     if task_id in download_manager.tasks:
         del download_manager.tasks[task_id]
         return {"status": "success", "message": "Download removed"}
@@ -115,7 +116,6 @@ async def cleanup_completed(
         count = download_manager.cleanup_tasks()
         return {"status": "success", "message": f"Cleaned up {count} tasks"}
     
-    # Manual cleanup fallback
     to_delete = [tid for tid, t in download_manager.tasks.items() if t.status == "completed"]
     for tid in to_delete:
         del download_manager.tasks[tid]