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>

contracts/protocols.py

@@ -5,6 +5,7 @@ implementations (Sql*Service) and no-op stubs both satisfy them.
 """
 from __future__ import annotations
 
+from datetime import datetime
 from typing import Protocol, runtime_checkable
 
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -27,6 +28,10 @@ class BlogService(Protocol):
     async def get_post_by_id(self, session: AsyncSession, id: int) -> PostDTO | None: ...
     async def get_posts_by_ids(self, session: AsyncSession, ids: list[int]) -> list[PostDTO]: ...
 
+    async def search_posts(
+        self, session: AsyncSession, query: str, page: int = 1, per_page: int = 10,
+    ) -> tuple[list[PostDTO], int]: ...
+
 
 @runtime_checkable
 class CalendarService(Protocol):
@@ -107,6 +112,16 @@ class CalendarService(Protocol):
         self, session: AsyncSession, user_id: int, session_id: str,
     ) -> None: ...
 
+    async def entry_ids_for_content(
+        self, session: AsyncSession, content_type: str, content_id: int,
+    ) -> set[int]: ...
+
+    async def visible_entries_for_period(
+        self, session: AsyncSession, calendar_id: int,
+        period_start: datetime, period_end: datetime,
+        *, user_id: int | None, is_admin: bool, session_id: str | None,
+    ) -> list[CalendarEntryDTO]: ...
+
 
 @runtime_checkable
 class MarketService(Protocol):