Add game version management system with manifest support

Features:
- Version dropdown in single/ZIP upload (9.3.0, 9.2.0, etc.)
- Patch-compatible matching (9.3.x assets work with 9.3.0)
- manifest.json/xml support for automatic metadata detection
- Smart category auto-detection from folder structure
- Version field stored in GameAssets table

Manifest support:
- JSON format with gameVersion, category, assets array
- Per-file metadata overrides (type, required, description)
- Auto-detect falls back if no manifest present
- See ASSET-MANIFEST-SPECIFICATION.md for full spec

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/obj/Debug/net8.0/RR3CommunityServer.sourcelink.json

@@ -1 +1 @@
-{"documents":{"E:\\rr3\\RR3CommunityServer\\*":"https://raw.githubusercontent.com/ssfdre38/rr3-server/15e842ce855b748cc97c43261eba408067128330/*"}}
+{"documents":{"E:\\rr3\\RR3CommunityServer\\*":"https://raw.githubusercontent.com/ssfdre38/rr3-server/f289cdfce9c28a229d8a00547a730c54530d68e9/*"}}