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>

events/bp/calendar/admin/routes.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from quart import (
-    request, Blueprint, g
+    Blueprint, g, request,
 )
 
 
@@ -15,18 +15,6 @@ from shared.sx.helpers import sx_response
 def register():
     bp = Blueprint("admin", __name__, url_prefix='/admin')
 
-    @bp.before_request
-    async def _prepare_page_data():
-        if "defpage_" not in (request.endpoint or ""):
-            return
-        from shared.sx.page import get_template_context
-        from sx.sx_components import _calendar_admin_main_panel_html
-        ctx = await get_template_context()
-        g.calendar_admin_content = _calendar_admin_main_panel_html(ctx)
-
-    from shared.sx.pages import mount_pages
-    mount_pages(bp, "events", names=["calendar-admin"])
-
     @bp.get("/description/")
     @require_admin
     async def calendar_description_edit(calendar_slug: str, **kwargs):