- Add _datetimeformat Jinja2 filter to _render_pattern() — templates
use {{ 'now' | datetimeformat('%Y') }} but the filter was never
registered, causing "No filter named 'datetimeformat'" on preview.
- Move Preview button to first column in template detail data table
so it's visible without scrolling on wide tables.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>