Add ai agent guidelines

AGENTS.md

@@ -0,0 +1,26 @@
+# ClusterCockpit Backend - Agent Guidelines
+
+## Build/Test Commands
+
+- Build: `make` or `go build ./cmd/cc-backend`
+- Run all tests: `make test` (runs: `go clean -testcache && go build ./... && go vet ./... && go test ./...`)
+- Run single test: `go test -run TestName ./path/to/package`
+- Run single test file: `go test ./path/to/package -run TestName`
+- Frontend build: `cd web/frontend && npm install && npm run build`
+- Generate GraphQL: `make graphql` (uses gqlgen)
+- Generate Swagger: `make swagger` (uses swaggo/swag)
+
+## Code Style
+
+- **Formatting**: Use `gofumpt` for all Go files (strict requirement)
+- **Copyright header**: All files must include copyright header (see existing files)
+- **Package docs**: Document packages with comprehensive package-level comments explaining purpose, usage, configuration
+- **Imports**: Standard library first, then external packages, then internal packages (grouped with blank lines)
+- **Naming**: Use camelCase for private, PascalCase for exported; descriptive names (e.g., `JobRepository`, `handleError`)
+- **Error handling**: Return errors, don't panic; use custom error types where appropriate; log with cclog package
+- **Logging**: Use `cclog` package (e.g., `cclog.Errorf()`, `cclog.Warnf()`, `cclog.Debugf()`)
+- **Testing**: Use standard `testing` package; use `testify/assert` for assertions; name tests `TestFunctionName`
+- **Comments**: Document all exported functions/types with godoc-style comments
+- **Structs**: Document fields with inline comments, especially for complex configurations
+- **HTTP handlers**: Return proper status codes; use `handleError()` helper for consistent error responses
+- **JSON**: Use struct tags for JSON marshaling; `DisallowUnknownFields()` for strict decoding