fix(story): replace datetime pickers with text fields for date inputs

Admin2's datetime widget ignores the blueprint format parameter and renders
dates in US MM/DD/YYYY locale format regardless. Switching both Start Date
and End Date to type:text eliminates the datepicker entirely — existing ISO
values (2025-09-06 20:00) display as typed, no locale interference.

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

themes/intotheeast/blueprints/story.yaml

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