Rename coop to blog throughout codebase

- coop_url() → blog_url(), AUTH_APP default → "blog"
- Session cookie: coop_session → blog_session
- Config keys: coop_root/coop_title → market_root/market_title
- All Jinja templates: coop_url → blog_url, coop_title → market_title
- Template blocks: coop-child-header → blog-child-header

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

infrastructure/factory.py

@@ -54,7 +54,7 @@ def create_base_app(
     context_fn:
         Async function returning a dict for template context.
         Each app provides its own — the cart app queries locally,
-        while coop/market apps fetch via internal API.
+        while blog/market apps fetch via internal API.
         If not provided, a minimal default context is used.
     before_request_fns:
         Extra before-request hooks (e.g. cart_loader for the cart app).
@@ -84,7 +84,7 @@ def create_base_app(
     cookie_domain = os.getenv("SESSION_COOKIE_DOMAIN")  # e.g. ".rose-ash.com"
     if cookie_domain:
         app.config["SESSION_COOKIE_DOMAIN"] = cookie_domain
-    app.config["SESSION_COOKIE_NAME"] = "coop_session"
+    app.config["SESSION_COOKIE_NAME"] = "blog_session"
 
     # Ghost / Redis config
     app.config["GHOST_API_URL"] = os.getenv("GHOST_API_URL")