feat: decouple blog from shared_lib, add app-owned models

Phase 1-3 of decoupling:
- path_setup.py adds project root to sys.path
- Blog-owned models in blog/models/ (ghost_content, snippet, tag_group)
- Re-export shims for shared models (user, kv, magic_link, menu_item)
- All imports updated: shared.infrastructure, shared.db, shared.browser, etc.
- No more cross-app post_id FKs in calendar/market/page_config

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

bp/blog/ghost/editor_api.py

@@ -13,7 +13,7 @@ import httpx
 from quart import Blueprint, request, jsonify, g
 from sqlalchemy import select, or_
 
-from suma_browser.app.authz import require_admin, require_login
+from shared.browser.app.authz import require_admin, require_login
 from models import Snippet
 from .ghost_admin_token import make_ghost_admin_jwt
 

bp/blog/ghost/ghost_sync.py

@@ -13,11 +13,11 @@ from sqlalchemy.orm.attributes import flag_modified  # for non-Mutable JSON colu
 from models.ghost_content import (
     Post, Author, Tag, PostAuthor, PostTag
 )
-from models.page_config import PageConfig
+from cart.models.page_config import PageConfig
 
 # User-centric membership models
-from models import User
-from models.ghost_membership_entities import (
+from shared.models import User
+from shared.models.ghost_membership_entities import (
     GhostLabel, UserLabel,
     GhostNewsletter, UserNewsletter,
     GhostTier, GhostSubscription,
@@ -29,7 +29,7 @@ from urllib.parse import quote
 
 GHOST_ADMIN_API_URL = os.environ["GHOST_ADMIN_API_URL"]
 
-from suma_browser.app.utils import (
+from shared.browser.app.utils import (
     utcnow
 )
 
@@ -242,10 +242,10 @@ async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[
     # Auto-create PageConfig for pages
     if obj.is_page:
         existing_pc = (await sess.execute(
-            select(PageConfig).where(PageConfig.post_id == obj.id)
+            select(PageConfig).where(PageConfig.container_type == "page", PageConfig.container_id == obj.id)
         )).scalar_one_or_none()
         if existing_pc is None:
-            sess.add(PageConfig(post_id=obj.id, features={}))
+            sess.add(PageConfig(container_type="page", container_id=obj.id, features={}))
             await sess.flush()
 
     return obj