Set page flag in sync_single_page to ensure is_page=true

Ghost /pages/ endpoint may not include "page": true in the response.
Explicitly set it so _upsert_post correctly marks is_page=true.

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

bp/blog/ghost/ghost_sync.py

@@ -1021,6 +1021,8 @@ async def sync_single_post(sess: AsyncSession, ghost_id: str) -> None:
 
 async def sync_single_page(sess: AsyncSession, ghost_id: str) -> None:
     gp = await fetch_single_page_from_ghost(ghost_id)
+    if gp is not None:
+        gp["page"] = True  # Ghost /pages/ endpoint may omit this flag
     if gp is None:
         res = await sess.execute(select(Post).where(Post.ghost_id == ghost_id))
         obj = res.scalar_one_or_none()