feat(channels): sort sidebar by latest activity, with favorite tier

Channels in the sidebar and mobile dropdown now sort by most recent
message first, with favorited channels pinned above non-favorites.
Reordering is push-driven via the existing new_message socket event:
the affected item is moved to the top of its tier in the DOM, no full
re-render. Favorites are toggled via a star icon in Manage Channels
and persisted in read_status.is_favorite for cross-device sync.

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

app/read_status.py

@@ -30,6 +30,7 @@ def load_read_status():
         channels = {}
         dm = {}
         muted_channels = []
+        favorite_channels = []
 
         for key, row in rows.items():
             if key.startswith('chan_'):
@@ -40,6 +41,11 @@ def load_read_status():
                         muted_channels.append(int(chan_idx))
                     except ValueError:
                         pass
+                if row.get('is_favorite'):
+                    try:
+                        favorite_channels.append(int(chan_idx))
+                    except ValueError:
+                        pass
             elif key.startswith('dm_'):
                 conv_id = key[3:]  # "dm_name_User1" -> "name_User1"
                 dm[conv_id] = row['last_seen_ts']
@@ -48,11 +54,12 @@ def load_read_status():
             'channels': channels,
             'dm': dm,
             'muted_channels': muted_channels,
+            'favorite_channels': favorite_channels,
         }
 
     except Exception as e:
         logger.error(f"Error loading read status: {e}")
-        return {'channels': {}, 'dm': {}, 'muted_channels': []}
+        return {'channels': {}, 'dm': {}, 'muted_channels': [], 'favorite_channels': []}
 
 
 def save_read_status(status):
@@ -126,6 +133,28 @@ def set_channel_muted(channel_idx, muted):
         return False
 
 
+def get_favorite_channels():
+    """Get list of favorite channel indices."""
+    try:
+        db = _get_db()
+        return db.get_favorite_channels()
+    except Exception as e:
+        logger.error(f"Error getting favorite channels: {e}")
+        return []
+
+
+def set_channel_favorite(channel_idx, favorite):
+    """Set favorite state for a channel."""
+    try:
+        db = _get_db()
+        db.set_channel_favorite(int(channel_idx), favorite)
+        logger.info(f"Channel {channel_idx} {'favorited' if favorite else 'unfavorited'}")
+        return True
+    except Exception as e:
+        logger.error(f"Error setting favorite for channel {channel_idx}: {e}")
+        return False
+
+
 def mark_all_channels_read(channel_timestamps):
     """Mark all channels as read in bulk.