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>

src/fabledassistant/services/weather.py

@@ -39,6 +39,13 @@ def describe_weathercode(code: int) -> str:
     return _WMO_CODES.get(code, f"Unknown (code {code})")
 
 
+async def get_temp_unit(user_id: int) -> str:
+    """Read the user's preferred temperature unit ('C' or 'F'), default 'C'."""
+    from fabledassistant.services.settings import get_setting
+    raw = await get_setting(user_id, "temp_unit", "C")
+    return raw if raw in ("C", "F") else "C"
+
+
 def parse_forecast(raw: dict) -> list[dict]:
     """Convert Open-Meteo daily response into a clean list of day dicts."""
     daily = raw.get("daily", {})