Add force update functionality for Ghost posts

- Add manual CI trigger 'force-update-ghost' for updating all posts
- Support FORCE_UPDATE environment variable in Rust code
- Implement post update logic via Ghost API PUT requests
- Add get_existing_post_id() function to find existing posts
- Update README with usage instructions
- Enhanced validation script to test new functionality

Usage:
- Normal: Only syncs new posts (default behavior)
- Force: FORCE_UPDATE=true updates ALL posts including existing ones

ghost-upload/README.md

@@ -1,3 +1,39 @@
 # ghost-upload
 
-This code uploads posts from https://projects.ansonbiggs.com to https://notes.ansonbiggs.com. I couldn't figure out how to update posts, and the kagi API doesn't make it clear how long it caches results for so for now only posts that don't exist on the ghost blog will be uploaded. If you want to update content you need to manually make edits to the code and delete posts on the blog.
+This tool synchronizes posts from https://projects.ansonbiggs.com to the Ghost blog at https://notes.ansonbiggs.com.
+
+## Features
+
+- **Automatic sync**: Only uploads new posts by default
+- **Content extraction**: Fetches clean HTML content instead of using iframes
+- **AI summaries**: Uses Kagi Summarizer for post summaries
+- **Force update**: Manual trigger to update all existing posts
+
+## Usage
+
+### Normal Mode (Default)
+```bash
+cargo run
+```
+Only processes new posts that don't exist on the Ghost blog.
+
+### Force Update Mode
+```bash
+FORCE_UPDATE=true cargo run
+```
+Updates ALL posts, including existing ones. Useful for:
+- Updating content after changes
+- Refreshing summaries
+- Applying new styling/formatting
+
+## CI/CD Integration
+
+The GitLab CI pipeline includes:
+- **Automatic sync**: Runs after each deployment
+- **Manual force update**: Available as a manual trigger in GitLab UI
+
+## Environment Variables
+
+- `admin_api_key`: Ghost Admin API key (required)
+- `kagi_api_key`: Kagi Summarizer API key (required)  
+- `FORCE_UPDATE`: Set to "true" to update all posts (optional)