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>

blog/sxc/pages/blog.sx

@@ -15,54 +15,54 @@
   :layout :blog
   :content (editor-page-content))
 
-; --- Post admin pages (nested under /<slug>/admin/) ---
+; --- Post admin pages (absolute paths under /<slug>/admin/) ---
 
 (defpage post-admin
-  :path "/"
+  :path "/<slug>/admin/"
   :auth :admin
   :layout (:post-admin :selected "admin")
-  :content (post-admin-content))
+  :content (post-admin-content slug))
 
 (defpage post-data
-  :path "/data/"
+  :path "/<slug>/admin/data/"
   :auth :admin
   :layout (:post-admin :selected "data")
-  :content (post-data-content))
+  :content (post-data-content slug))
 
 (defpage post-preview
-  :path "/preview/"
+  :path "/<slug>/admin/preview/"
   :auth :admin
   :layout (:post-admin :selected "preview")
-  :content (post-preview-content))
+  :content (post-preview-content slug))
 
 (defpage post-entries
-  :path "/entries/"
+  :path "/<slug>/admin/entries/"
   :auth :admin
   :layout (:post-admin :selected "entries")
-  :content (post-entries-content))
+  :content (post-entries-content slug))
 
 (defpage post-settings
-  :path "/settings/"
+  :path "/<slug>/admin/settings/"
   :auth :post_author
   :layout (:post-admin :selected "settings")
-  :content (post-settings-content))
+  :content (post-settings-content slug))
 
 (defpage post-edit
-  :path "/edit/"
+  :path "/<slug>/admin/edit/"
   :auth :post_author
   :layout (:post-admin :selected "edit")
-  :content (post-edit-content))
+  :content (post-edit-content slug))
 
-; --- Settings pages ---
+; --- Settings pages (absolute paths) ---
 
 (defpage settings-home
-  :path "/"
+  :path "/settings/"
   :auth :admin
   :layout :blog-settings
   :content (settings-content))
 
 (defpage cache-page
-  :path "/cache/"
+  :path "/settings/cache/"
   :auth :admin
   :layout :blog-cache
   :content (cache-content))
@@ -70,7 +70,7 @@
 ; --- Snippets ---
 
 (defpage snippets-page
-  :path "/"
+  :path "/settings/snippets/"
   :auth :login
   :layout :blog-snippets
   :content (snippets-content))
@@ -78,7 +78,7 @@
 ; --- Menu Items ---
 
 (defpage menu-items-page
-  :path "/"
+  :path "/settings/menu_items/"
   :auth :admin
   :layout :blog-menu-items
   :content (menu-items-content))
@@ -86,13 +86,13 @@
 ; --- Tag Groups ---
 
 (defpage tag-groups-page
-  :path "/"
+  :path "/settings/tag-groups/"
   :auth :admin
   :layout :blog-tag-groups
   :content (tag-groups-content))
 
 (defpage tag-group-edit
-  :path "/<int:id>/"
+  :path "/settings/tag-groups/<int:id>/"
   :auth :admin
   :layout :blog-tag-group-edit
-  :content (tag-group-edit-content))
+  :content (tag-group-edit-content id))