Auto-mount defpages: eliminate Python route stubs across all 9 services

Defpages are now declared with absolute paths in .sx files and auto-mounted
directly on the Quart app, removing ~850 lines of blueprint mount_pages calls,
before_request hooks, and g.* wrapper boilerplate. A new page = one defpage
declaration, nothing else.

Infrastructure:
- async_eval awaits coroutine results from callable dispatch
- auto_mount_pages() mounts all registered defpages on the app
- g._defpage_ctx pattern passes helper data to layout context

Migrated: sx, account, orders, federation, cart, market, events, blog

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

cart/bp/cart/global_routes.py

@@ -56,9 +56,9 @@ def register(url_prefix: str) -> Blueprint:
 
         if request.headers.get("SX-Request") == "true" or request.headers.get("HX-Request") == "true":
             # Redirect to overview for HTMX
-            return redirect(url_for("cart_overview.defpage_cart_overview"))
+            return redirect(url_for("defpage_cart_overview"))
 
-        return redirect(url_for("cart_overview.defpage_cart_overview"))
+        return redirect(url_for("defpage_cart_overview"))
 
     @bp.post("/quantity/<int:product_id>/")
     async def update_quantity(product_id: int):
@@ -137,7 +137,7 @@ def register(url_prefix: str) -> Blueprint:
         tickets = await get_ticket_cart_entries(g.s)
 
         if not cart and not calendar_entries and not tickets:
-            return redirect(url_for("cart_overview.defpage_cart_overview"))
+            return redirect(url_for("defpage_cart_overview"))
 
         product_total = total(cart) or 0
         calendar_amount = calendar_total(calendar_entries) or 0
@@ -145,7 +145,7 @@ def register(url_prefix: str) -> Blueprint:
         cart_total = product_total + calendar_amount + ticket_amount
 
         if cart_total <= 0:
-            return redirect(url_for("cart_overview.defpage_cart_overview"))
+            return redirect(url_for("defpage_cart_overview"))
 
         try:
             page_config = await resolve_page_config(g.s, cart, calendar_entries, tickets)