feat(briefing): hard-cut tear-down

Backend:
- Delete briefing services (pipeline, scheduler, conversations, profile, tools)
- Delete routes/briefing.py + remove blueprint registration
- Move _get_temp_unit into services/weather.get_temp_unit (reads top-level temp_unit setting)
- Rename briefing_preferences.py → rss_filtering.py (functions are RSS-specific)
- Strip briefing scheduler hooks from app.py
- Strip briefing scheduler call from routes/settings.py
- Update test imports (test_rss_service, test_tz_helpers)

Frontend:
- Delete BriefingView, BriefingSetupWizard, BriefingToolStatusRow
- Strip /briefing route + nav links (AppHeader, KnowledgeView)
- Strip Settings → Briefing tab + state + functions + imports
- Strip briefing-intermediate handling from ChatMessage
- Hide /news route + nav links (NewsView depended on briefing endpoints; orphaned in tree)
- Drop unused useSettingsStore from AppHeader

The Android BriefingScreen lives in a separate repo and is not touched here.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_tz_helpers.py

@@ -26,12 +26,12 @@ async def test_get_user_tz_falls_back_to_utc_on_bad_input():
 
 
 @pytest.mark.asyncio
-async def test_user_briefing_date_before_4am_returns_yesterday():
-    """00:00–03:59 local still shows yesterday's briefing day."""
+async def test_user_day_date_before_4am_returns_yesterday():
+    """00:00–03:59 local still shows yesterday's day_date."""
     from fabledassistant.services import tz as tz_mod
 
     ny = ZoneInfo("America/New_York")
-    # 02:00 NY on 2026-04-13 → briefing day = 2026-04-12
+    # 02:00 NY on 2026-04-13 → day_date = 2026-04-12 (still pre-rollover)
     fake_now = datetime(2026, 4, 13, 2, 0, tzinfo=ny)
 
     class _FakeDatetime(datetime):
@@ -41,12 +41,12 @@ async def test_user_briefing_date_before_4am_returns_yesterday():
 
     with patch.object(tz_mod, "get_user_tz", AsyncMock(return_value=ny)), \
          patch.object(tz_mod, "datetime", _FakeDatetime):
-        day = await tz_mod.user_briefing_date(1)
+        day = await tz_mod.user_day_date(1)
     assert day.isoformat() == "2026-04-12"
 
 
 @pytest.mark.asyncio
-async def test_user_briefing_date_after_4am_returns_today():
+async def test_user_day_date_after_4am_returns_today():
     from fabledassistant.services import tz as tz_mod
 
     ny = ZoneInfo("America/New_York")
@@ -59,5 +59,5 @@ async def test_user_briefing_date_after_4am_returns_today():
 
     with patch.object(tz_mod, "get_user_tz", AsyncMock(return_value=ny)), \
          patch.object(tz_mod, "datetime", _FakeDatetime):
-        day = await tz_mod.user_briefing_date(1)
+        day = await tz_mod.user_day_date(1)
     assert day.isoformat() == "2026-04-13"