fix(story): restore datetime type, use date-only format; strip times from demo stories

Reverts text→datetime change. Uses format:'Y-m-d' (date-only) so the
datepicker omits the time component. Strips HH:MM from all Italy demo
story dates for consistency with the new date-only format.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

themes/intotheeast/blueprints/story.yaml

@@ -18,18 +18,17 @@ form:
                 required: true
 
             header.date:
-              type: text
+              type: datetime
               label: Start Date
-              placeholder: '2025-09-06 20:00'
-              help: 'Format: YYYY-MM-DD HH:MM'
+              format: 'Y-m-d'
               validate:
                 required: true
 
             header.end_date:
-              type: text
+              type: datetime
               label: End Date
-              placeholder: '2025-09-12'
-              help: 'Format: YYYY-MM-DD — leave blank for a single-day story'
+              format: 'Y-m-d'
+              help: 'Optional — leave blank for a single-day story'
 
             header.hero_image:
               type: text