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>

shared/sx/pages.py

@@ -290,6 +290,18 @@ async def execute_page(
 # Blueprint mounting
 # ---------------------------------------------------------------------------
 
+def auto_mount_pages(app: Any, service_name: str) -> None:
+    """Auto-mount all registered defpages for a service directly on the app.
+
+    Pages must have absolute paths (from the service URL root).
+    Called once per service in app.py after setup_*_pages().
+    """
+    pages = get_all_pages(service_name)
+    for page_def in pages.values():
+        _mount_one_page(app, service_name, page_def)
+    logger.info("Auto-mounted %d defpages for %s", len(pages), service_name)
+
+
 def mount_pages(bp: Any, service_name: str,
                 names: set[str] | list[str] | None = None) -> None:
     """Mount registered PageDef routes onto a Quart Blueprint.