fix(story): smart date range formatting + blueprint end_date format fix

Blueprint: end_date format changed from 'Y-m-d H:i' to 'Y-m-d' — the
demo frontmatter stores dates without a time component so Admin was
failing to parse it and showing the field empty.

Template: three-case smart range formatting:
- Same month & year  → 01 – 03 Sep 2025
- Same year only     → 01 Jan – 03 Sep 2025
- Different years    → 01 Jan 2025 – 03 Feb 2026

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

themes/intotheeast/blueprints/story.yaml

@@ -27,7 +27,7 @@ form:
             header.end_date:
               type: datetime
               label: End Date
-              format: 'Y-m-d H:i'
+              format: 'Y-m-d'
               help: 'Optional — leave blank for a single-day story'
 
             header.hero_image: