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/database.py

@@ -62,6 +62,12 @@ class Database:
             conn.execute("ALTER TABLE echoes ADD COLUMN hash_size INTEGER NOT NULL DEFAULT 1")
             logger.info("Migration: added echoes.hash_size column")
 
+        # Add is_favorite column to read_status (channel favorites)
+        rs_columns = {r[1] for r in conn.execute("PRAGMA table_info(read_status)").fetchall()}
+        if 'is_favorite' not in rs_columns:
+            conn.execute("ALTER TABLE read_status ADD COLUMN is_favorite INTEGER DEFAULT 0")
+            logger.info("Migration: added read_status.is_favorite column")
+
     @contextmanager
     def _connect(self):
         """Yield a connection with auto-commit/rollback."""
@@ -1130,6 +1136,26 @@ class Database:
             ).fetchall()
             return [int(r['key'][5:]) for r in rows]
 
+    def set_channel_favorite(self, channel_idx: int, favorite: bool) -> None:
+        key = f"chan_{channel_idx}"
+        with self._connect() as conn:
+            conn.execute(
+                """INSERT INTO read_status (key, is_favorite)
+                   VALUES (?, ?)
+                   ON CONFLICT(key) DO UPDATE SET
+                       is_favorite = excluded.is_favorite,
+                       updated_at = datetime('now')""",
+                (key, 1 if favorite else 0)
+            )
+
+    def get_favorite_channels(self) -> List[int]:
+        """Get list of favorite channel indices."""
+        with self._connect() as conn:
+            rows = conn.execute(
+                "SELECT key FROM read_status WHERE is_favorite = 1 AND key LIKE 'chan_%'"
+            ).fetchall()
+            return [int(r['key'][5:]) for r in rows]
+
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