Remove cross-domain template dependencies from shared infrastructure

- macros/search.html: shared search input macros (mobile + desktop)
- macros/cart_icon.html: shared cart icon/badge macro (count param, no DB)
- macros/layout.html: inline hamburger icon, use shared search macro
- _oob.html: use cart_mini_html fragment slot instead of cart template import
- db/session.py: guard teardown rollback against committed/dead sessions

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

db/session.py

@@ -64,11 +64,17 @@ def register_db(app: Quart):
             # If an exception occurred OR we didn't commit (still in txn), roll back.
             if hasattr(g, "s"):
                 if exc is not None or g.s.in_transaction():
-                    if hasattr(g, "tx"):
-                        await g.tx.rollback()
+                    if hasattr(g, "tx") and g.tx.is_active:
+                        try:
+                            await g.tx.rollback()
+                        except Exception:
+                            pass
         finally:
             if hasattr(g, "s"):
-                await g.s.close()
+                try:
+                    await g.s.close()
+                except Exception:
+                    pass
 
     @app.errorhandler(Exception)
     async def mark_error(e):