docs: update Go code style guidelines and linting requirements

- Enhanced AGENTS.md to include post-editing commands for Go code, specifying the use of `gofmt -w`, `go vet ./...`, and `scripts/lint-go.ps1`.
- Updated engineering rules in .cursor/rules/engineering.mdc to clarify the linting process and ensure consistency in Go code formatting.
- Improved documentation for CI checks related to Go code style and linting.

scripts/lint-go.ps1

@@ -0,0 +1,19 @@
+# Same gates as CI job go (subset): gofmt, vet, golangci-lint.
+$ErrorActionPreference = 'Stop'
+Set-Location (Join-Path $PSScriptRoot '..')
+
+$unfmt = gofmt -l . 2>$null
+if ($unfmt) {
+  Write-Error "gofmt: unformatted files:`n$unfmt"
+}
+go vet ./...
+$golangci = Get-Command golangci-lint -ErrorAction SilentlyContinue
+if (-not $golangci) {
+  $golangciPath = Join-Path $env:USERPROFILE 'go\bin\golangci-lint.exe'
+  if (Test-Path $golangciPath) { $golangci = @{ Source = $golangciPath } }
+}
+if ($golangci) {
+  & $golangci.Source run
+} else {
+  Write-Warning 'lint-go: golangci-lint not found, skipping (CI will run it)'
+}