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/bp/page_markets/routes.py

@@ -2,55 +2,40 @@
 Page-markets blueprint — shows markets for a single page.
 
 Mounted at /<slug> (page-scoped). Requires g.post_data from hydrate_post.
-
-Routes:
-  GET  /<slug>/              — full page scoped to this page
-  GET  /<slug>/page-markets  — HTMX fragment for infinite scroll
+GET / handled by defpage. GET /page-markets is pagination fragment.
 """
 from __future__ import annotations
 
-from quart import Blueprint, g, request, render_template, make_response
+from quart import Blueprint, g, request
 
-from shared.browser.app.utils.htmx import is_htmx_request
 from shared.sx.helpers import sx_response
 from shared.services.registry import services
 
 
+async def _load_markets(post_id, page, per_page=20):
+    """Load markets for this page's container."""
+    markets, has_more = await services.market.list_marketplaces(
+        g.s, "page", post_id, page=page, per_page=per_page,
+    )
+    return markets, has_more
+
+
 def register() -> Blueprint:
     bp = Blueprint("page_markets", __name__)
 
-    async def _load_markets(post_id, page, per_page=20):
-        """Load markets for this page's container."""
-        markets, has_more = await services.market.list_marketplaces(
-            g.s, "page", post_id, page=page, per_page=per_page,
-        )
-        return markets, has_more
-
-    @bp.get("/")
-    async def index():
+    @bp.before_request
+    async def _prepare_page_data():
+        """Load page-markets data for defpage routes."""
+        endpoint = request.endpoint or ""
+        if not endpoint.endswith("defpage_page_markets_index"):
+            return
         post = g.post_data["post"]
         page = int(request.args.get("page", 1))
-
         markets, has_more = await _load_markets(post["id"], page)
-
-        ctx = dict(
-            markets=markets,
-            has_more=has_more,
-            page_info={},
-            page=page,
-        )
-
-        from shared.sx.page import get_template_context
-        from sx.sx_components import render_page_markets_page, render_page_markets_oob
-
-        tctx = await get_template_context()
-        tctx["post"] = post
-        if is_htmx_request():
-            sx_src = await render_page_markets_oob(tctx, markets, has_more, page)
-            return sx_response(sx_src)
-        else:
-            html = await render_page_markets_page(tctx, markets, has_more, page)
-            return await make_response(html, 200)
+        g.page_markets_data = {
+            "markets": markets, "has_more": has_more,
+            "page": page, "post_slug": post.get("slug", ""),
+        }
 
     @bp.get("/page-markets")
     async def markets_fragment():