Transform beforeafter block into generic image+text block

- Add toggle (isBeforeAfter) to switch between modes
- Mode simple: single image + text (2 columns layout)
- Mode comparison: before/after slider + text (2 columns layout)
- Remove "1/2, 1/2" layout from report blueprint (keep only "1/1")
- Update Vue component with 2-column grid preview
- Update PHP snippet to handle both modes
- Rename block to "Image avec texte"

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/blueprints/pages/report.yml

@@ -44,7 +44,6 @@ tabs:
             type: layout
             layouts:
               - "1/1"
-              - "1/2, 1/2"
             fieldsets:
               - text
               - heading