docs: add CLAUDE.md for Claude Code guidance

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.
+
+## Critical Rules
+
+**These rules override all other instructions:**
+
+1. **NEVER commit directly to main** - Always create a feature branch and submit a pull request
+2. **Conventional commits** - Format: `type(scope): description`
+3. **GitHub Issues for TODOs** - Use `gh` CLI to manage issues, no local TODO files. Use conventional commit format for issue titles
+4. **Pull Request titles** - Use conventional commit format (same as commits)
+5. **Branch naming** - Use format: `type/short-description` (e.g., `feat/settings-dialog`)
+6. **Working an issue** - Always create a new branch from an updated main branch
+7. **Check branch status before pushing** - Verify the remote tracking branch still exists. If a PR was merged/deleted, create a new branch from main instead
+
+---
+
+### GitHub CLI Commands
+
+```bash
+gh issue list                    # List open issues
+gh issue view <number>           # View details
+gh issue create --title "type(scope): description" --body "..."
+gh issue close <number>
+```
+
+### Conventional Commit Types
+
+| Type | Description |
+|------|-------------|
+| `feat` | New feature |
+| `fix` | Bug fix |
+| `docs` | Documentation only |
+| `refactor` | Code change that neither fixes a bug nor adds a feature |
+| `test` | Adding or updating tests |
+| `chore` | Maintenance tasks |
+| `perf` | Performance improvement |
+| `ci` | CI/CD changes |
+
+---
+
+## Project Overview
+
+This is a GitHub Action (`CodingWithCalvin/GHA-VSVsixVersioner`) that versions Visual Studio extensions (.vsix) using a date-based versioning scheme: `YYYY.M.D.BuildNumber`. It updates both the XML manifest (`source.extension.vsixmanifest`) and the C# code-behind file (`source.extension.cs`) that are synchronized via VSIX Synchronizer.
+
+**Important**: This action only runs on Windows-based GitHub runners.
+
+## Commands
+
+```bash
+# Install dependencies
+npm ci
+
+# Run tests
+npm test
+
+# Run a single test file
+npx jest __tests__/main.test.ts
+
+# Run tests with pattern matching
+npx jest -t "test name pattern"
+
+# Lint
+npm run lint
+
+# Format code
+npm run format:write
+
+# Check formatting without changes
+npm run format:check
+
+# Build/package the action
+npm run package
+
+# Full build (format, lint, test, coverage, package)
+npm run all
+```
+
+## Architecture
+
+Single-file TypeScript GitHub Action (`src/index.ts`) bundled with `@vercel/ncc` to `dist/index.js`.
+
+**Flow:**
+1. Reads `extension-manifest-file` and `extension-source-file` inputs (required)
+2. Generates version string: `YYYY.M.D.{build-number}` (build-number defaults to `github.context.runNumber`)
+3. Parses XML manifest with `fast-xml-parser`, updates `PackageManifest.Metadata.Identity[@Version]`
+4. Updates C# source file by replacing `Version = "x.x.x.x";` pattern via regex
+5. Outputs the generated `version` for downstream steps
+
+**Key dependencies:**
+- `@actions/core` - GitHub Action I/O and failure handling
+- `@actions/github` - GitHub context (run number)
+- `fast-xml-parser` - XML parsing/building for vsixmanifest
+
+## Configuration
+
+- ESLint config: `.github/linters/.eslintrc.yml`
+- Jest config: embedded in `package.json`
+- TypeScript: `tsconfig.json` (ES2022, NodeNext modules, strict mode)
+- Node version: specified in `.node-version` file (requires Node >= 21)