Phase 7: Replace render_template() with s-expression rendering in all POST/PUT/DELETE routes

Eliminates all render_template() calls from POST/PUT/DELETE handlers across
all 7 services. Moves sexp_components.py into sexp/ packages per service.

- Blog: like toggle, snippets, cache clear, features/sumup/entry panels,
  create/delete market, WYSIWYG editor panel (render_editor_panel)
- Federation: like/unlike/boost/unboost, follow/unfollow, actor card,
  interaction buttons
- Events: ticket widget, checkin, confirm/decline/provisional, tickets
  config, posts CRUD, description edit/save, calendar/slot/ticket_type
  CRUD, payments, buy tickets, day main panel, entry page
- Market: like toggle, cart add response
- Account: newsletter toggle
- Cart: checkout error pages (3 handlers)
- Orders: checkout error page (1 handler)

Remaining render_template() calls are exclusively in GET handlers and
internal services (email templates, fragment endpoints).

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

orders/bp/order/routes.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from quart import Blueprint, g, render_template, redirect, url_for, make_response
+from quart import Blueprint, g, redirect, url_for, make_response
 from sqlalchemy import select
 from sqlalchemy.orm import selectinload
 
@@ -48,7 +48,7 @@ def register() -> Blueprint:
         if not order:
             return await make_response("Order not found", 404)
 
-        from sexp_components import render_order_page, render_order_oob
+        from sexp.sexp_components import render_order_page, render_order_oob
 
         ctx = await get_template_context()
         calendar_entries = ctx.get("calendar_entries")
@@ -98,11 +98,10 @@ def register() -> Blueprint:
         await g.s.flush()
 
         if not hosted_url:
-            html = await render_template(
-                "_types/cart/checkout_error.html",
-                order=order,
-                error="No hosted checkout URL returned from SumUp when trying to reopen payment.",
-            )
+            from shared.sexp.page import get_template_context
+            from sexp.sexp_components import render_checkout_error_page
+            tctx = await get_template_context()
+            html = await render_checkout_error_page(tctx, error="No hosted checkout URL returned from SumUp when trying to reopen payment.", order=order)
             return await make_response(html, 500)
 
         return redirect(hosted_url)

orders/bp/orders/routes.py

@@ -117,7 +117,7 @@ def register(url_prefix: str) -> Blueprint:
         orders = result.scalars().all()
 
         from shared.sexp.page import get_template_context
-        from sexp_components import (
+        from sexp.sexp_components import (
             render_orders_page,
             render_orders_rows,
             render_orders_oob,