Add Asset Download System with CDN Support

ASSET CONTENT DELIVERY:
+ ContentController.cs
  - Serves game assets (cars, tracks, textures, audio)
  - Downloads from EA CDN (while available)
  - Caches for offline serving
  - Manifest endpoint for asset lists
  - Health check endpoint

FEATURES:
- Asset manifest (/synergy/content/manifest)
- Download assets (/synergy/content/download/{type}/{id})
- Asset metadata (/synergy/content/info/{type}/{id})
- List by type (/synergy/content/list/{type})
- Status checking (HEAD requests)
- MD5 checksums for integrity
- Automatic directory structure

STORAGE:
+ Assets/ directory with structure:
  - cars/
  - tracks/
  - textures/
  - audio/
+ README.md - Complete asset guide
+ .gitignore - Excludes .pak files (copyrighted)

DIRECTOR UPDATE:
* DirectorController.cs
  - Added synergy.content URL
  - Game will request assets from community server

DOCUMENTATION:
+ Assets/README.md
  - How to extract assets
  - Legal guidelines (preservation only)
  - Testing instructions
  - Asset formats and naming

PURPOSE:
Game preservation after EA shutdown.
Users extract assets they own, server hosts them.
Post-shutdown: Full offline gameplay possible.

LEGAL:
- For preservation of owned content only
- Do not distribute EA's copyrighted assets
- Private server use

This enables complete game functionality
independent of EA's servers! 🎮

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

RR3CommunityServer/obj/Debug/net8.0/RR3CommunityServer.csproj.CoreCompileInputs.cache

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