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>

events/bp/markets/routes.py

@@ -9,9 +9,8 @@ from .services.markets import (
     soft_delete as svc_soft_delete,
 )
 
-from shared.browser.app.redis_cacher import cache_page, clear_cache
+from shared.browser.app.redis_cacher import clear_cache
 from shared.browser.app.authz import require_admin
-from shared.browser.app.utils.htmx import is_htmx_request
 from shared.sx.helpers import sx_response
 
 
@@ -22,18 +21,17 @@ def register():
     async def inject_root():
         return {}
 
-    @bp.get("/")
-    async def home(**kwargs):
+    @bp.before_request
+    async def _prepare_page_data():
+        if "defpage_" not in (request.endpoint or ""):
+            return
         from shared.sx.page import get_template_context
-        from sx.sx_components import render_markets_page, render_markets_oob
-
+        from sx.sx_components import _markets_main_panel_html
         ctx = await get_template_context()
-        if not is_htmx_request():
-            html = await render_markets_page(ctx)
-            return await make_response(html)
-        else:
-            sx_src = await render_markets_oob(ctx)
-            return sx_response(sx_src)
+        g.markets_content = _markets_main_panel_html(ctx)
+
+    from shared.sx.pages import mount_pages
+    mount_pages(bp, "events", names=["events-markets"])
 
     @bp.post("/new/")
     @require_admin