feat: add smart PR preview deployment system (#38)

* fix: ensure PRs are added to project with correct status

- Update sync-labels-to-project.yml to handle pull_request events
- Add new workflow to automatically add PRs to project when opened
- Create script to fix status for existing PRs in project

This ensures:
1. New PRs are automatically added to the project
2. PR status labels (pr-in-progress, in-code-review, etc.) sync to project fields
3. Existing PRs can be fixed with the cleanup script

* feat: add smart PR preview deployment system

- Create smart deployment workflow that only deploys for relevant changes
- Skip deployment for docs, workflows, scripts, and other non-demo changes
- Add manual control via labels (deploy-preview, skip-preview)
- Add slash commands (/preview, /skip-preview) for manual control
- Auto-detect and communicate deployment decisions
- Add documentation for the new system

Benefits:
- Faster CI by skipping unnecessary deployments
- Cost savings on Cloudflare resources
- Cleaner PR threads with less noise
- Manual override when needed

* fix: correct fork detection and prevent duplicate skip comments

- Fix fork detection logic in smart preview workflow
- Only show skip comment when PR is first opened, not on every sync
- This prevents the spam of 'PRs from forks cannot be auto-deployed' messages

* fix: resolve flaky test for notEqual operator in DateFilter

- Add explicit wait for state to settle after setting model
- Fixes race condition in CI where validation state might not be ready
- Test was passing in isolation but failing in full test suite

Author: ryanrozich