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>

shared/sexp/page.py

@@ -83,9 +83,9 @@ async def get_template_context(**kwargs: Any) -> dict[str, Any]:
             ctx.update(rv)
 
     # Inject Jinja globals that s-expression components need (URL helpers,
-    # asset_url, site, etc.) — these aren't provided by context processors.
+    # asset_url, styles, etc.) — these aren't provided by context processors.
     for key, val in current_app.jinja_env.globals.items():
-        if key not in ctx and callable(val):
+        if key not in ctx:
             ctx[key] = val
 
     ctx.update(kwargs)