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>

market/bp/all_markets/routes.py

@@ -41,19 +41,6 @@ async def _load_markets(page, per_page=20):
 def register() -> Blueprint:
     bp = Blueprint("all_markets", __name__)
 
-    @bp.before_request
-    async def _prepare_page_data():
-        """Load all-markets data for defpage routes."""
-        endpoint = request.endpoint or ""
-        if not endpoint.endswith("defpage_all_markets_index"):
-            return
-        page = int(request.args.get("page", 1))
-        markets, has_more, page_info = await _load_markets(page)
-        g.all_markets_data = {
-            "markets": markets, "has_more": has_more,
-            "page_info": page_info, "page": page,
-        }
-
     @bp.get("/all-markets")
     async def markets_fragment():
         page = int(request.args.get("page", 1))