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/all_events/routes.py

@@ -11,7 +11,7 @@ Routes:
 """
 from __future__ import annotations
 
-from quart import Blueprint, g, request, render_template, make_response
+from quart import Blueprint, g, request, make_response
 
 from shared.browser.app.utils.htmx import is_htmx_request
 from shared.sx.helpers import sx_response