feat: Add SendVid downloader support

Add complete support for SendVid video hosting service used by Anime-Sama
for anime series like Hell's Paradise.

Changes:
- Create SendVidDownloader class with proper headers to avoid 403 errors
- Add SendVid detection and handling in AnimeSamaDownloader
- Update download_manager to include SendVid-specific headers
- Support custom episode naming (e.g., "Hells Paradise - Episode 01.mp4")

Technical details:
- SendVid embed pages require User-Agent and Referer headers
- Direct MP4 URLs extracted from <source> tags with IP/time-based parameters
- Tested with Hell's Paradise Episode 01 (7MB, 24min, 1280x720)

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

app/downloaders/__init__.py

@@ -0,0 +1,48 @@
+from .base import BaseDownloader
+from .unfichier import UnFichierDownloader
+from .doodstream import DoodStreamDownloader
+from .rapidfile import RapidFileDownloader
+from .uptobox import UptoboxDownloader
+from .animesama import AnimeSamaDownloader
+from .animeultime import AnimeUltimeDownloader
+from .nekosama import NekoSamaDownloader
+from .vostfree import VostfreeDownloader
+from .vidmoly import VidMolyDownloader
+from .sendvid import SendVidDownloader
+
+
+def get_downloader(url: str) -> BaseDownloader:
+    """Factory function to get the appropriate downloader for a URL"""
+    downloaders = [
+        # Anime sites
+        AnimeSamaDownloader(),
+        AnimeUltimeDownloader(),
+        NekoSamaDownloader(),
+        VostfreeDownloader(),
+        # File hosts
+        UnFichierDownloader(),
+        UptoboxDownloader(),
+        DoodStreamDownloader(),
+        RapidFileDownloader(),
+        VidMolyDownloader(),
+        SendVidDownloader(),
+    ]
+
+    for downloader in downloaders:
+        if downloader.can_handle(url):
+            return downloader
+
+    # Return generic downloader if no match
+    return GenericDownloader()
+
+
+class GenericDownloader(BaseDownloader):
+    """Generic downloader for unhandled hosts"""
+
+    def can_handle(self, url: str) -> bool:
+        return True
+
+    async def get_download_link(self, url: str) -> tuple[str, str]:
+        # Just return the URL as-is
+        filename = url.split('/')[-1] or "download"
+        return url, filename