Replace env free-variable threading with IO-primitive auto-fetch macros

Layout components now self-resolve context (cart-mini, auth-menu, nav-tree,
rights, URLs) via new IO primitives (root-header-ctx, select-colours,
account-nav-ctx, app-rights) and defmacro wrappers (~root-header-auto,
~auth-header-row-auto, ~root-mobile-auto). This eliminates _ctx_to_env(),
HELPER_CSS_CLASSES, and verbose :key threading across all 10 services.

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

events/sxc/pages/slots.py

@@ -1,7 +1,6 @@
 """Slot panels, forms, edit/add, slot picker JS."""
 from __future__ import annotations
 
-from markupsafe import escape
 
 from shared.sx.helpers import render_to_sx
 from shared.sx.parser import SxExpr
@@ -156,20 +155,12 @@ async def _slot_header_html(ctx: dict, *, oob: bool = False) -> str:
     if not slot:
         return ""
 
-    # Label: icon + name + description
     desc = getattr(slot, "description", "") or ""
-    label_inner = (
-        f'<div class="flex flex-col md:flex-row md:gap-2 items-center">'
-        f'<div class="flex flex-row items-center gap-2">'
-        f'<i class="fa fa-clock"></i>'
-        f'<div class="shrink-0">{escape(slot.name)}</div>'
-        f'</div>'
-        f'<p class="text-stone-500 whitespace-pre-line break-all w-full">{escape(desc)}</p>'
-        f'</div>'
-    )
+    label_sx = await render_to_sx("events-slot-label",
+                                  name=slot.name, description=desc)
 
     return await render_to_sx("menu-row-sx", id="slot-row", level=5,
-                  link_label_content=SxExpr(label_inner),
+                  link_label_content=SxExpr(label_sx),
                   child_id="slot-header-child", oob=oob)