Fix duplicate menu rows on HTMX navigation between depth levels

When navigating from a deeper page (e.g. day) to a shallower one
(e.g. calendar) via HTMX, orphaned header rows from the deeper page
persisted in the DOM because OOB swaps only replaced specific child
divs, not siblings. Fix by sending empty OOB swaps to clear all
header row IDs not present at the current depth.

Applied to events (calendars/calendar/day/entry/admin/slots) and
market (market_home/browse/product/admin). Also restore app_label
in root header.

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

shared/sexp/helpers.py

@@ -41,6 +41,7 @@ def root_header_html(ctx: dict, *, oob: bool = False) -> str:
         cart_mini_html=ctx.get("cart_mini_html", ""),
         blog_url=call_url(ctx, "blog_url", ""),
         site_title=ctx.get("base_title", ""),
+        app_label=ctx.get("app_label", ""),
         nav_tree_html=ctx.get("nav_tree_html", ""),
         auth_menu_html=ctx.get("auth_menu_html", ""),
         nav_panel_html=ctx.get("nav_panel_html", ""),