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>

.env.example

@@ -0,0 +1,13 @@
+# Ohm Streaming API Configuration
+
+# Server
+HOST=0.0.0.0
+PORT=8000
+RELOAD=true
+
+# Paths
+UPLOAD_DIR=uploads
+STREAM_DIR=streams
+
+# CORS
+ALLOWED_ORIGINS=*