ci: fix NuGet cache path with NUGET_PACKAGES env var

- Add NUGET_PACKAGES env var at job level to pin package cache location
- Change cache path from ~/.nuget/packages to runner.temp/.nuget/packages
- Add id to cache steps and diagnostic 'Cache status' step to show hit/miss
- Add DOTNET_NOLOGO and DOTNET_CLI_TELEMETRY_OPT_OUT for cleaner logs
- Applied to build, test, and release jobs uniformly

.gitignore

@@ -45,3 +45,4 @@ Desktop.ini
 
 # Internal dev memory (stays local, not published)
 memory-bank/
+memorybank.md