Fix unknown sender names in Bluesky chats, reduce false notifications, and reorder Chats buffer

Resolve sender DIDs to display names by building member maps from conversation
data. Fix compose functions to prefer snake_case attributes (ATProto SDK convention).
Ensure stable key comparison in dedup logic by converting ATProto objects to strings.
Move Chats buffer to appear after Mentions and before Notifications.

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

src/sessions/blueski/session.py

@@ -751,6 +751,18 @@ class Session(base.baseSession):
             log.exception("Error listing conversations")
             return {"items": [], "cursor": None}
 
+    def get_convo(self, convo_id: str):
+        """Fetch a single conversation by ID, returning the convo object or None."""
+        api = self._ensure_client()
+        dm_client = api.with_bsky_chat_proxy()
+        dm = dm_client.chat.bsky.convo
+        try:
+            res = dm.get_convo({"convoId": convo_id})
+            return res.convo
+        except Exception:
+            log.exception("Error fetching conversation %s", convo_id)
+            return None
+
     def get_convo_messages(self, convo_id: str, limit: int = 50, cursor: str | None = None) -> dict[str, Any]:
         api = self._ensure_client()
         dm_client = api.with_bsky_chat_proxy()