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>

events/bp/calendars/routes.py

@@ -36,7 +36,7 @@ def register():
     @cache_page(tag="calendars")
     async def home(**kwargs):
         from shared.sexp.page import get_template_context
-        from sexp_components import render_calendars_page, render_calendars_oob
+        from sexp.sexp_components import render_calendars_page, render_calendars_oob
 
         ctx = await get_template_context()
         if not is_htmx_request():
@@ -68,13 +68,15 @@ def register():
         except Exception as e:
             return await make_response(f'<div class="text-red-600 text-sm">{e}</div>', 422)
 
-        html = await render_template(
-            "_types/calendars/index.html",
-        )
+        from shared.sexp.page import get_template_context
+        from sexp.sexp_components import render_calendars_list_panel
+        ctx = await get_template_context()
+        html = render_calendars_list_panel(ctx)
 
         # Blog-embedded mode: also update post nav
         if post_data:
             from shared.services.entry_associations import get_associated_entries
+            from sexp.sexp_components import render_post_nav_entries_oob
 
             cals = (
                 await g.s.execute(
@@ -85,14 +87,7 @@ def register():
             ).scalars().all()
 
             associated_entries = await get_associated_entries(g.s, post_id)
-
-            nav_oob = await render_template(
-                "_types/post/admin/_nav_entries_oob.html",
-                associated_entries=associated_entries,
-                calendars=cals,
-                post=post_data["post"],
-            )
-
+            nav_oob = render_post_nav_entries_oob(associated_entries, cals, post_data["post"])
             html = html + nav_oob
 
         return await make_response(html)