Fix 500 errors and double-slash URLs found during sexp rendering testing

- events: fix ImportError for events_url (was importing from shared.utils
  instead of shared.infrastructure.urls)
- blog: add missing ~mobile-filter sexp component (details/summary panel)
- shared: fix double-slash URLs in ~auth-menu, ~cart-mini, ~header-row
  by removing redundant "/" concatenation on URLs that already have trailing slash
- blog: fix ghost_sync select UnboundLocalError caused by redundant local
  import shadowing module-level import

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

blog/bp/blog/ghost/ghost_sync.py

@@ -251,7 +251,6 @@ async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[
     # Auto-create PageConfig for pages (blog owns this table — direct DB,
     # not via HTTP, since this may run during startup before the server is ready)
     if obj.is_page:
-        from sqlalchemy import select
         from shared.models.page_config import PageConfig
         existing = (await sess.execute(
             select(PageConfig).where(