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/bp/snippets/routes.py

@@ -1,11 +1,9 @@
 from __future__ import annotations
 
-from quart import Blueprint, make_response, request, g, abort
+from quart import Blueprint, request, g, abort
 from sqlalchemy import select, or_
-from sqlalchemy.orm import selectinload
 
 from shared.browser.app.authz import require_login
-from shared.browser.app.utils.htmx import is_htmx_request
 from shared.sx.helpers import sx_response
 from models import Snippet
 
@@ -32,22 +30,6 @@ async def _visible_snippets(session):
 def register():
     bp = Blueprint("snippets", __name__, url_prefix="/settings/snippets")
 
-    @bp.before_request
-    async def _prepare_page_data():
-        if "defpage_" not in (request.endpoint or ""):
-            return
-        snippets = await _visible_snippets(g.s)
-        is_admin = g.rights.get("admin")
-        from shared.sx.page import get_template_context
-        from sx.sx_components import _snippets_main_panel_sx
-        tctx = await get_template_context()
-        tctx["snippets"] = snippets
-        tctx["is_admin"] = is_admin
-        g.snippets_content = _snippets_main_panel_sx(tctx)
-
-    from shared.sx.pages import mount_pages
-    mount_pages(bp, "blog", names=["snippets-page"])
-
     @bp.delete("/<int:snippet_id>/")
     @require_login
     async def delete_snippet(snippet_id: int):