docs: add CLAUDE.md for Claude Code guidance

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+A Kubernetes controller that automatically creates `LimitRange` resources (named `extreme-request-defaults`) in all non-excluded namespaces to set default memory requests for containers. Runs as a loop checking every 10 seconds.
+
+## Build Commands
+
+```bash
+# Run tests
+go test -race -coverprofile=coverage.txt ./...
+
+# Check for vulnerabilities
+go install golang.org/x/vuln/cmd/govulncheck@latest
+govulncheck ./...
+
+# Build binary
+CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o release/default-request-adder -ldflags '-w -s'
+
+# Build Docker image (uses build-tools, not buildx)
+docker build -t default-request-adder .
+```
+
+## Architecture
+
+Single-file Go application (`main.go`) that:
+- Uses in-cluster Kubernetes client configuration (`rest.InClusterConfig()`)
+- Loops through all namespaces every 10 seconds
+- Creates `LimitRange` named `extreme-request-defaults` in non-excluded namespaces
+- Deletes the `LimitRange` from excluded namespaces if present
+
+### CLI Flags
+- `-excluded-ns`: Comma-separated list of namespaces to exclude (default: `kube-system`). Use `*` to exclude all.
+- `-memory`: Default memory request value (default: `1Ti`)
+
+## CI/CD
+
+- **Gitea Actions**: `.gitea/workflows/ci.yaml` - runs tests and vulnerability checks
+- **GitLab CI**: `.gitlab-ci.yml` - uses `buildtool/build-tools` for builds
+- **Releases**: Uses git-cliff for changelog generation (see `cliff.toml`)