Add Game Asset Preservation System Foundation

DATABASE SCHEMA:
+ GameAsset entity added to RR3DbContext
  - Asset identification (ID, type, filename)
  - EA CDN tracking (original URL, CDN path)
  - Local storage (path, size, SHA256)
  - Metadata (downloads, access count, timestamps)
  - Game-specific (carId, trackId, category)

FEATURES:
- Track all cached assets in database
- Store EA CDN URLs while available
- SHA256 integrity checking
- Access statistics
- Category organization
- Version tracking

PURPOSE:
Foundation for full asset caching system.
Next step: AssetsController with EA CDN proxying.

STORAGE STRUCTURE:
wwwroot/assets/
├── cars/
├── tracks/
├── textures/
├── audio/
├── models/
└── misc/

PRESERVATION STRATEGY:
Phase 1 (EA online): Proxy + cache assets
Phase 2 (EA offline): Serve from cache
Result: Complete game preservation! 🎮💾

Package added: Microsoft.Extensions.Http (for CDN proxying)

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

RR3CommunityServer/obj/Debug/net8.0/RR3CommunityServer.AssemblyInfo.cs

@@ -13,7 +13,7 @@ using System.Reflection;
 [assembly: System.Reflection.AssemblyCompanyAttribute("RR3CommunityServer")]
 [assembly: System.Reflection.AssemblyConfigurationAttribute("Debug")]
 [assembly: System.Reflection.AssemblyFileVersionAttribute("1.0.0.0")]
-[assembly: System.Reflection.AssemblyInformationalVersionAttribute("1.0.0+934fa5152419080c5b5141b2593477e484c01afe")]
+[assembly: System.Reflection.AssemblyInformationalVersionAttribute("1.0.0+3970ecd9a37b28b51f913c1e0ab5a41f4a7c69d0")]
 [assembly: System.Reflection.AssemblyProductAttribute("RR3CommunityServer")]
 [assembly: System.Reflection.AssemblyTitleAttribute("RR3CommunityServer")]
 [assembly: System.Reflection.AssemblyVersionAttribute("1.0.0.0")]