fix: sync header_style DB column with theme editor selections (#158)

The frontend never sent header_style/hero_divider_style as separate
fields when creating or updating events, so the database columns always
kept their default value of 'standard' — making the hero header
impossible to enable through the admin UI.

- Extract headerStyle/heroDividerStyle from theme config and include in
  create and update payloads (CreateEventPage, EventDetailsPage)
- Add backend fallback to extract values from color_theme JSON when not
  explicitly provided, ensuring older clients stay in sync

.gitignore

@@ -86,6 +86,14 @@ docs/*_PLAN.md
 docs/test-*.md
 docs/feature-*.md
 
+# Scaffolding documentation (local development reference)
+docs/DATABASE_SCHEMA.md
+docs/BACKEND_SERVICES.md
+docs/API_ROUTES.md
+docs/FRONTEND_ARCHITECTURE.md
+docs/DEVELOPER_ONBOARDING.md
+docs/ENVIRONMENT_VARIABLES.md
+
 # Local backup directory (from testing)
 backup/