feat: temperature unit preference and slot timezone display for briefing

- Add °C/°F toggle in briefing settings; persisted in briefing_config.temp_unit
- briefing_pipeline reads temp_unit and converts Open-Meteo Celsius values
  before passing them to the LLM (both full compilation and slot injection)
- Scheduled Slots section now shows each UTC slot time converted to the
  user's browser local time, plus a line confirming which timezone the
  browser is using

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

src/fabledassistant/services/briefing_pipeline.py

@@ -192,16 +192,26 @@ def _internal_user_prompt(data: dict, slot: str) -> str:
     return "\n".join(lines)
 
 
-def _external_user_prompt(data: dict, slot: str) -> str:
+def _format_temp(value: float, unit: str) -> str:
+    """Convert Celsius to the requested unit and format as an integer string."""
+    if unit == "F":
+        return f"{value * 9 / 5 + 32:.0f}"
+    return f"{value:.0f}"
+
+
+def _external_user_prompt(data: dict, slot: str, temp_unit: str = "C") -> str:
+    unit_sym = f"°{temp_unit}"
     lines = [f"Briefing slot: {slot}", ""]
     if data["weather"]:
         lines.append("WEATHER:")
         for loc in data["weather"]:
             lines.append(f"  {loc['location_label']}:")
             for day in loc["days"][:3]:
+                t_min = _format_temp(day["temp_min"], temp_unit)
+                t_max = _format_temp(day["temp_max"], temp_unit)
                 lines.append(
                     f"    {day['date']}: {day['description']}, "
-                    f"{day['temp_min']}–{day['temp_max']}°C, {day['precip_mm']}mm rain"
+                    f"{t_min}–{t_max}{unit_sym}, {day['precip_mm']}mm rain"
                 )
             if loc["changes_since_last_fetch"]:
                 lines.append("  FORECAST CHANGES:")
@@ -218,6 +228,18 @@ def _external_user_prompt(data: dict, slot: str) -> str:
 
 # ── Main entry point ───────────────────────────────────────────────────────────
 
+async def _get_temp_unit(user_id: int) -> str:
+    """Read the user's preferred temperature unit from briefing_config ('C' or 'F')."""
+    import json
+    raw = await get_setting(user_id, "briefing_config", "{}")
+    try:
+        config = json.loads(raw) if isinstance(raw, str) else (raw or {})
+        unit = config.get("temp_unit", "C")
+        return unit if unit in ("C", "F") else "C"
+    except Exception:
+        return "C"
+
+
 async def run_compilation(user_id: int, slot: str, model: str | None = None) -> str:
     """
     Run the full two-lane briefing pipeline for a user and slot.
@@ -227,7 +249,10 @@ async def run_compilation(user_id: int, slot: str, model: str | None = None) ->
         model = await get_setting(user_id, "default_model", Config.OLLAMA_MODEL)
 
     from fabledassistant.services.briefing_profile import get_profile_body
-    profile_body = await get_profile_body(user_id)
+    profile_body, temp_unit = await asyncio.gather(
+        get_profile_body(user_id),
+        _get_temp_unit(user_id),
+    )
 
     # Parallel gather
     internal_data, external_data = await asyncio.gather(
@@ -244,7 +269,7 @@ async def run_compilation(user_id: int, slot: str, model: str | None = None) ->
         ),
         _llm_synthesise(
             _external_system_prompt(),
-            _external_user_prompt(external_data, slot),
+            _external_user_prompt(external_data, slot, temp_unit),
             model,
         ),
     )
@@ -268,9 +293,10 @@ async def run_slot_injection(user_id: int, slot: str, model: str | None = None)
     if model is None:
         model = await get_setting(user_id, "default_model", Config.OLLAMA_MODEL)
 
-    internal_data, external_data = await asyncio.gather(
+    internal_data, external_data, temp_unit = await asyncio.gather(
         _gather_internal(user_id),
         _gather_external(user_id),
+        _get_temp_unit(user_id),
     )
 
     system = (
@@ -281,6 +307,6 @@ async def run_slot_injection(user_id: int, slot: str, model: str | None = None)
         f"Slot: {slot}\n\n"
         + _internal_user_prompt(internal_data, slot)
         + "\n\n"
-        + _external_user_prompt(external_data, slot)
+        + _external_user_prompt(external_data, slot, temp_unit)
     )
     return await _llm_synthesise(system, user_prompt, model)