Migrate all apps to defpage declarative page routes

Replace Python GET page handlers with declarative defpage definitions in .sx
files across all 8 apps (sx docs, orders, account, market, cart, federation,
events, blog). Each app now has sxc/pages/ with setup functions, layout
registrations, page helpers, and .sx defpage declarations.

Core infrastructure: add g I/O primitive, PageDef support for auth/layout/
data/content/filter/aside/menu slots, post_author auth level, and custom
layout registration. Remove ~1400 lines of render_*_page/render_*_oob
boilerplate. Update all endpoint references in routes, sx_components, and
templates to defpage_* naming.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

market/app.py

@@ -99,25 +99,30 @@ def create_app() -> "Quart":
         app.jinja_loader,
     ])
 
+    # Setup defpage routes
+    from sxc.pages import setup_market_pages
+    setup_market_pages()
+
+    from shared.sx.pages import mount_pages
+
     # All markets: / — global view across all pages
-    app.register_blueprint(
-        register_all_markets(),
-        url_prefix="/",
-    )
+    all_markets_bp = register_all_markets()
+    mount_pages(all_markets_bp, "market", names=["all-markets-index"])
+    app.register_blueprint(all_markets_bp, url_prefix="/")
 
     # Page markets: /<slug>/ — markets for a single page
-    app.register_blueprint(
-        register_page_markets(),
-        url_prefix="/<slug>",
-    )
+    page_markets_bp = register_page_markets()
+    mount_pages(page_markets_bp, "market", names=["page-markets-index"])
+    app.register_blueprint(page_markets_bp, url_prefix="/<slug>")
 
     # Page admin: /<slug>/admin/ — post-level admin for markets
-    app.register_blueprint(
-        register_page_admin(),
-        url_prefix="/<slug>/admin",
-    )
+    page_admin_bp = register_page_admin()
+    mount_pages(page_admin_bp, "market", names=["page-admin"])
+    app.register_blueprint(page_admin_bp, url_prefix="/<slug>/admin")
 
     # Market blueprint nested under post slug: /<page_slug>/<market_slug>/
+    # Defpages for market-home and market-admin are mounted inside their
+    # respective nested blueprints (browse and admin register functions).
     app.register_blueprint(
         register_market_bp(
             url_prefix="/",