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>

account/bp/account/routes.py

@@ -8,7 +8,6 @@ from __future__ import annotations
 from quart import (
     Blueprint,
     request,
-    render_template,
     make_response,
     redirect,
     g,
@@ -48,7 +47,7 @@ def register(url_prefix="/"):
     async def account():
         from shared.browser.app.utils.htmx import is_htmx_request
         from shared.sexp.page import get_template_context
-        from sexp_components import render_account_page, render_account_oob
+        from sexp.sexp_components import render_account_page, render_account_oob
 
         if not g.get("user"):
             return redirect(login_url("/"))
@@ -90,7 +89,7 @@ def register(url_prefix="/"):
             })
 
         from shared.sexp.page import get_template_context
-        from sexp_components import render_newsletters_page, render_newsletters_oob
+        from sexp.sexp_components import render_newsletters_page, render_newsletters_oob
 
         ctx = await get_template_context()
         if not is_htmx_request():
@@ -125,10 +124,8 @@ def register(url_prefix="/"):
 
         await g.s.flush()
 
-        return await render_template(
-            "_types/auth/_newsletter_toggle.html",
-            un=un,
-        )
+        from sexp.sexp_components import render_newsletter_toggle
+        return render_newsletter_toggle(un)
 
     # Catch-all for fragment-provided pages — must be last
     @account_bp.get("/<slug>/")
@@ -147,7 +144,7 @@ def register(url_prefix="/"):
             abort(404)
 
         from shared.sexp.page import get_template_context
-        from sexp_components import render_fragment_page, render_fragment_oob
+        from sexp.sexp_components import render_fragment_page, render_fragment_oob
 
         ctx = await get_template_context()
         if not is_htmx_request():