feat: Add AGENTS.md and new downloaders with metadata enrichment

- Add AGENTS.md for agentic coding guidelines
- Add Oneupload and Smoothpre video player downloaders
- Add MetadataEnrichment service with Kitsu API fallback
- Add tests for metadata enrichment and provider detection
- Update .gitignore to ignore runtime config files

.gitignore

@@ -45,3 +45,12 @@ favorites.json
 *.db
 *.sqlite
 ohm_streaming.db
+
+# Config (runtime-generated)
+config/anime_sama_domain.json
+config/metadata_cache.json
+data/
+favorites.json
+*.db
+*.sqlite
+ohm_streaming.db