Fix database bugs and add comprehensive test report 🔧📋

Bugs Fixed:
- Fixed SQLite missing column errors (Cash, Gold, Level, etc.)
- Fixed LINQ translation error in AssetsController (File.Exists)
- Fixed type mismatch in ModdingController (null coalescing)
- Applied database migrations for complete schema

Database Changes:
- Added User currency columns (Gold, Cash, Level, XP, Reputation)
- Added Car custom content fields (IsCustom, CustomAuthor, CustomVersion)
- Added GameAsset metadata fields (Md5Hash, CompressedSize)
- Added ModPacks table for mod bundling

Testing:
- Comprehensive test report: COMPREHENSIVE_TEST_REPORT.md
- 9/9 critical endpoints passing
- All APK-required functionality verified
- Database operations validated
- Response format compatibility confirmed

Status: ✅ Server is production-ready (pending assets)

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

RR3CommunityServer/Controllers/AssetsController.cs

@@ -176,8 +176,14 @@ public class AssetsController : ControllerBase
     public async Task<ActionResult<SynergyResponse<object>>> GetStatus()
     {
         var totalAssets = await _context.GameAssets.CountAsync();
-        var availableAssets = await _context.GameAssets
-            .CountAsync(a => !string.IsNullOrEmpty(a.LocalPath) && System.IO.File.Exists(a.LocalPath));
+        
+        // Get all assets with LocalPath, then check file existence in memory
+        var assetsWithPath = await _context.GameAssets
+            .Where(a => !string.IsNullOrEmpty(a.LocalPath))
+            .Select(a => a.LocalPath)
+            .ToListAsync();
+        
+        var availableAssets = assetsWithPath.Count(path => System.IO.File.Exists(path));
 
         var categoryCounts = await _context.GameAssets
             .GroupBy(a => a.Category)