docs: add project guidelines for Claude Code (#4)

## Summary
- Add CLAUDE.md with project guidelines
- Documents conventional commit format and types
- Specifies branch naming conventions
- Includes PR management instructions using tea CLI

## Test plan
- Review CLAUDE.md content
- Verify formatting and accuracy

Reviewed-on: #4
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

CLAUDE.md

@@ -0,0 +1,44 @@
+# Guide To `lambda`
+
+Absolutely NO advertisement of Claude.
+
+## Coding Styles
+
+### Conventional Commits
+
+Use conventional commit format: `<type>: <description>`.
+
+**Types**: `feat`, `fix`, `docs`, `refactor`, `test`, `chore`, `perf`
+
+**Examples**:
+
+- `feat: add explanation mode flag to CLI`
+- `fix: correct variable renaming in nested abstractions`
+- `docs: update Makefile documentation`
+
+### Branch Names
+
+Use format: `<type>/<description>` with kebab-case.
+
+**Types**: Same as commits: `feat`, `fix`, `docs`, `refactor`, `test`, `chore`, `perf`.
+
+**Examples**:
+
+- `feat/explanation-mode`
+- `fix/variable-renaming`
+- `docs/makefile-improvements`
+- `refactor/silent-directive`
+
+## Pull Request Management
+
+Use the `tea` CLI (Gitea command-line tool) for PR operations instead of `gh`.
+
+**Common commands**:
+
+- `tea pr create` - Create a new pull request.
+- `tea pr list` - List pull requests.
+- `tea pr checkout <number>` - Check out a PR locally.
+- `tea pr close <number>` - Close a pull request.
+- `tea pr merge <number>` - Merge a pull request.
+
+**Creating PRs**: Always create PRs in a branch other than `main`, to the `main` branch unless specified otherwise.