Fix cross-DB queries: move page_configs to cart, fix OAuth code_hash lookup

page_configs table lives in db_cart but blog was querying it directly,
causing UndefinedTableError. Move all PageConfig read/write endpoints to
cart service and have blog proxy via fetch_data/call_action.

Also fix OAuth callback to use code_hash lookup (codes are now stored
hashed) and pass grant_token in redirect URL to prevent auth loops.

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

blog/bp/post/services/markets.py

@@ -3,12 +3,11 @@ from __future__ import annotations
 import re
 import unicodedata
 
-from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from shared.models.page_config import PageConfig
 from shared.contracts.dtos import MarketPlaceDTO
 from shared.infrastructure.actions import call_action, ActionError
+from shared.infrastructure.data_client import fetch_data
 from shared.services.registry import services
 
 
@@ -42,10 +41,10 @@ async def create_market(sess: AsyncSession, post_id: int, name: str) -> MarketPl
     if not post.is_page:
         raise MarketError("Markets can only be created on pages, not posts.")
 
-    pc = (await sess.execute(
-        select(PageConfig).where(PageConfig.container_type == "page", PageConfig.container_id == post_id)
-    )).scalar_one_or_none()
-    if pc is None or not (pc.features or {}).get("market"):
+    raw_pc = await fetch_data("cart", "page-config",
+        params={"container_type": "page", "container_id": post_id},
+        required=False)
+    if raw_pc is None or not (raw_pc.get("features") or {}).get("market"):
         raise MarketError("Market feature is not enabled for this page. Enable it in page settings first.")
 
     try: