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/slots/routes.py

@@ -38,18 +38,6 @@ def register():
           }
       return {"slots": []}
 
-    @bp.before_request
-    async def _prepare_page_data():
-        if "defpage_" not in (request.endpoint or ""):
-            return
-        calendar = getattr(g, "calendar", None)
-        slots = await svc_list_slots(g.s, calendar.id) if calendar else []
-        from sx.sx_components import render_slots_table
-        g.slots_content = render_slots_table(slots, calendar)
-
-    from shared.sx.pages import mount_pages
-    mount_pages(bp, "events", names=["slots-listing"])
-
     @bp.post("/")
     @require_admin
     @clear_cache(tag="calendars", tag_scope="all")