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>

requirements.txt

@@ -0,0 +1,11 @@
+fastapi==0.115.6
+uvicorn[standard]==0.32.1
+python-multipart==0.0.20
+aiofiles==24.1.0
+pydantic==2.10.4
+pydantic-settings==2.7.1
+httpx==0.28.1
+aiohttp==3.11.11
+beautifulsoup4==4.12.3
+lxml==5.3.0
+jieba==0.42.1