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/sxc/pages/market.sx

@@ -1,10 +1,10 @@
 ;; Market app defpage declarations.
 ;;
 ;; all-markets-index: / — global view across all pages
-;; page-markets-index: / (on page_markets bp, mounted at /<slug>)
-;; page-admin: / (on page_admin bp, mounted at /<slug>/admin)
-;; market-home: / (on browse bp, mounted at /<page_slug>/<market_slug>)
-;; market-admin: / (on admin bp, mounted at /<page_slug>/<market_slug>/admin)
+;; page-markets-index: /<slug>/ — markets for a single page
+;; page-admin: /<slug>/admin/ — post-level admin for markets
+;; market-home: /<page_slug>/<market_slug>/ — market landing page
+;; market-admin: /<page_slug>/<market_slug>/admin/ — market admin
 
 (defpage all-markets-index
   :path "/"
@@ -13,25 +13,25 @@
   :content (all-markets-content))
 
 (defpage page-markets-index
-  :path "/"
+  :path "/<slug>/"
   :auth :public
   :layout :post
   :content (page-markets-content))
 
 (defpage page-admin
-  :path "/"
+  :path "/<slug>/admin/"
   :auth :admin
   :layout (:post-admin :selected "markets")
   :content (page-admin-content))
 
 (defpage market-home
-  :path "/"
+  :path "/<page_slug>/<market_slug>/"
   :auth :public
   :layout :market
   :content (market-home-content))
 
 (defpage market-admin
-  :path "/"
+  :path "/<page_slug>/<market_slug>/admin/"
   :auth :admin
   :layout (:market-admin :selected "markets")
   :content (market-admin-content))