fix: use jsonb cast and EXISTS in page_configs migration

PostgreSQL json type doesn't support equality operators needed by
DISTINCT. Use EXISTS subquery instead and cast to jsonb.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic/versions/a1b2c3d4e5f6_add_page_configs_table.py

@@ -37,19 +37,21 @@ def upgrade() -> None:
     # 1. Pages with calendars -> features={"calendar": true}
     conn.execute(text("""
         INSERT INTO page_configs (post_id, features, created_at, updated_at)
-        SELECT DISTINCT p.id, '{"calendar": true}'::json, now(), now()
+        SELECT p.id, '{"calendar": true}'::jsonb, now(), now()
         FROM posts p
-        JOIN calendars c ON c.post_id = p.id
         WHERE p.is_page = true
           AND p.deleted_at IS NULL
-          AND c.deleted_at IS NULL
+          AND EXISTS (
+              SELECT 1 FROM calendars c
+              WHERE c.post_id = p.id AND c.deleted_at IS NULL
+          )
     """))
 
     # 2. Market page (slug='market', is_page=true) -> features={"market": true}
     #    Only if not already inserted above
     conn.execute(text("""
         INSERT INTO page_configs (post_id, features, created_at, updated_at)
-        SELECT p.id, '{"market": true}'::json, now(), now()
+        SELECT p.id, '{"market": true}'::jsonb, now(), now()
         FROM posts p
         WHERE p.slug = 'market'
           AND p.is_page = true
@@ -60,7 +62,7 @@ def upgrade() -> None:
     # 3. All other pages -> features={}
     conn.execute(text("""
         INSERT INTO page_configs (post_id, features, created_at, updated_at)
-        SELECT p.id, '{}'::json, now(), now()
+        SELECT p.id, '{}'::jsonb, now(), now()
         FROM posts p
         WHERE p.is_page = true
           AND p.deleted_at IS NULL