feat: enforce calendar creation only on pages with calendar feature

Calendar creation now requires the parent post to be a page (is_page=True)
with the calendar feature enabled in its PageConfig. Update shared_lib
submodule with PageConfig model.

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

bp/calendars/services/calendars.py

@@ -5,6 +5,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from models.calendars import Calendar
 from models.ghost_content import Post  # for FK existence checks
+from models.page_config import PageConfig
 import unicodedata
 import re
 
@@ -79,10 +80,20 @@ async def create_calendar(sess: AsyncSession, post_id: int, name: str) -> Calend
     slug=slugify(name)
 
     # Ensure post exists (avoid silent FK errors in some DBs)
-    post = (await sess.execute(select(Post.id).where(Post.id == post_id))).scalar_one_or_none()
+    post = (await sess.execute(select(Post).where(Post.id == post_id))).scalar_one_or_none()
     if not post:
         raise CalendarError(f"Post {post_id} does not exist.")
 
+    # Enforce: calendars can only be created on pages with the calendar feature
+    if not post.is_page:
+        raise CalendarError("Calendars can only be created on pages, not posts.")
+
+    pc = (await sess.execute(
+        select(PageConfig).where(PageConfig.post_id == post_id)
+    )).scalar_one_or_none()
+    if pc is None or not (pc.features or {}).get("calendar"):
+        raise CalendarError("Calendar feature is not enabled for this page. Enable it in page settings first.")
+
     # Look for existing (including soft-deleted)
     q = await sess.execute(
         select(Calendar).where(Calendar.post_id == post_id, Calendar.name == name)