fix: resolve intermittent build failures in CI workflows

Root causes identified and fixed:

1. AirAppHost recursive build issue:
   - Main project triggers AirAppHost build as post-build step
   - AirAppHost references main project, creating circular dependency
   - Added SkipAirAppHostBuild=true to build.yml to break the cycle
   - Release workflow handles AirAppHost separately in publish step

2. NuGet cache path issues:
   - Changed from relative path (.nuget/packages) to absolute path
   - Added NUGET_PACKAGES environment variable with github.workspace
   - Added actions/cache for NuGet packages across all workflows

3. Missing NuGet package caching:
   - Added actions/cache@v4 with proper cache keys
   - Cache key based on Directory.Packages.props hash
   - Fallback restore keys for partial cache hits

These changes should eliminate the intermittent failures caused by:
- File locking conflicts from recursive builds
- Path resolution inconsistencies
- Network-dependent package downloads on every build

.github/workflows/release.yml

@@ -20,6 +20,8 @@ env:
   DOTNET_VERSION: '10.0.x'
   Solution_Name: LanMountainDesktop.slnx
   DOTNET_gcServer: 1
+  # Use absolute path for NuGet cache to avoid path resolution issues
+  NUGET_PACKAGES: ${{ github.workspace }}/.nuget/packages
 
 jobs:
   prepare:
@@ -437,6 +439,14 @@ jobs:
           dotnet-version: ${{ env.DOTNET_VERSION }}
           dotnet-quality: 'preview'
 
+      - name: Cache NuGet packages
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}/.nuget/packages
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/Directory.Packages.props') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget-
+
       - name: Stamp release version metadata
         shell: pwsh
         run: |