Add project guide documentation for Safari CDN status extension

Provides comprehensive project overview, including:
- Key files and their purposes
- Testing instructions
- Release process for GitHub and App Store
- Versioning strategy
- Project structure
- Supported CDNs

This documentation helps developers understand the project setup, workflow, and technical details.

Author: bartTC

CLAUDE.md

@@ -0,0 +1,79 @@
+# Project Guide
+
+Safari extension that displays CDN cache status (HIT/MISS) for the current page.
+
+## Key Files
+
+| File | Purpose |
+|------|---------|
+| `CHANGELOG.md` | Technical changelog for developers |
+| `RELEASE_NOTES.md` | User-facing release notes (App Store "What's New") |
+| `RELEASE.md` | Full release documentation and workflow |
+| `PRIVACY.md` | Privacy policy |
+| `scripts/config.sh` | Shared config (APP_NAME, PROJECT, SCHEME) |
+
+## Testing
+
+```bash
+just test    # Run CDN detection tests (27 test cases)
+```
+
+Tests are in `tests/cdn-detection.test.js` and validate all CDN detection rules in `constants.js`.
+
+## Release Process
+
+### Direct Distribution (GitHub)
+
+```bash
+git tag v0.0.X
+git push origin v0.0.X
+just release v0.0.X        # Archive and submit for notarization
+just status                # Check notarization status
+just staple                # After approval: staple ticket
+just dmg                   # Create DMG installer
+gh release create v0.0.X   # Create GitHub release with assets
+```
+
+### App Store
+
+```bash
+just release-appstore v0.0.X   # Archive and upload to App Store Connect
+```
+
+Then submit for review in App Store Connect.
+
+## Versioning
+
+- **Git tag is the single source of truth**
+- `MARKETING_VERSION` auto-derived from tag (v0.0.8 → 0.0.8)
+- `CURRENT_PROJECT_VERSION` (build number) = git commit count
+- No manual Xcode version updates needed
+
+## Project Structure
+
+```
+CF Cache Status/
+├── CF Cache Status/              # macOS container app (SwiftUI)
+└── CF Cache Status Extension/    # Safari Web Extension
+    └── Resources/
+        ├── manifest.json         # Extension config
+        ├── constants.js          # CDN detection rules
+        ├── background.js         # Header capture
+        └── popup.js/html/css     # Popup UI
+
+scripts/
+├── config.sh                     # Shared variables
+├── archive.sh                    # Build for direct distribution
+├── archive-appstore.sh           # Build for App Store
+├── submit.sh                     # Submit for notarization
+├── staple.sh                     # Staple and create zip
+└── create-dmg.sh                 # Create DMG installer
+
+Justfile                          # Build commands
+```
+
+## Supported CDNs
+
+Cloudflare, CloudFront, Fastly, Akamai, Bunny CDN, Varnish, and any CDN using x-cache headers.
+
+Detection rules are in `constants.js`.