Decoupling audit cleanup: fix protocol gaps, remove dead APIs

- Add search_posts, entry_ids_for_content, visible_entries_for_period
  to protocols and stubs
- Delete internal_api.py and factory cleanup hook (zero callers)
- Convert utils.py to utils/ package with calendar_helpers module
- Remove deleted_at check from calendar_view template (service filters)

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

browser/templates/_types/post/admin/_calendar_view.html

@@ -30,7 +30,7 @@
             {# Entries for this day #}
             <div class="space-y-0.5">
               {% for e in month_entries %}
-                {% if e.start_at.date() == day.date and e.deleted_at is none %}
+                {% if e.start_at.date() == day.date %}
                   {% if e.id in associated_entry_ids %}
                     {# Associated entry - show with delete button #}
                     <div class="flex items-center gap-1 text-[10px] rounded px-1 py-0.5 bg-green-200 text-green-900">