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>

blog/bp/menu_items/routes.py

@@ -12,7 +12,6 @@ from .services.menu_items import (
     search_pages,
     MenuItemError,
 )
-from shared.browser.app.utils.htmx import is_htmx_request
 from shared.sx.helpers import sx_response
 
 def register():
@@ -23,20 +22,6 @@ def register():
         from sx.sx_components import render_menu_items_nav_oob
         return render_menu_items_nav_oob(menu_items)
 
-    @bp.before_request
-    async def _prepare_page_data():
-        if "defpage_" not in (request.endpoint or ""):
-            return
-        menu_items = await get_all_menu_items(g.s)
-        from shared.sx.page import get_template_context
-        from sx.sx_components import _menu_items_main_panel_sx
-        tctx = await get_template_context()
-        tctx["menu_items"] = menu_items
-        g.menu_items_content = _menu_items_main_panel_sx(tctx)
-
-    from shared.sx.pages import mount_pages
-    mount_pages(bp, "blog", names=["menu-items-page"])
-
     @bp.get("/new/")
     @require_admin
     async def new_menu_item():