fix: center minichat widget and fix weather tool success status

- KnowledgeView minichat: add margin-inline: auto so the widget centers
  within the content area when max-width is reached on wide screens
- weather get_weather tool: return success: true on both the arbitrary
  location path and the cached locations path so ToolCallCard shows
  the correct success state instead of always flagging as error

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

src/fabledassistant/services/tools.py

@@ -1923,7 +1923,7 @@ async def execute_tool(
                     lat, lon, label = await geocode(location)
                     raw = await _fetch_open_meteo(lat, lon)
                     days = parse_forecast(raw)
-                    return {"data": {"locations": [{
+                    return {"success": True, "data": {"locations": [{
                         "location_key": "query",
                         "location_label": label,
                         "fetched_at": datetime.now(_tz.utc).isoformat(),
@@ -1936,7 +1936,7 @@ async def execute_tool(
             locations = await get_cached_weather(user_id)
             if location.lower() not in ("all", ""):
                 locations = [loc for loc in locations if loc["location_key"] == location.lower()]
-            return {"data": {"locations": locations}}
+            return {"success": True, "data": {"locations": locations}}
 
         elif tool_name == "get_rss_items":
             from fabledassistant.services.rss import get_recent_items