core/agent: fix Phase A streaming await bug and polish

Do not await async generators for raw SSE; close stream on cancel;
merge tool calls without relying only on finish_reason; quieter tool
output; /status slash command.

src/plyngent/agent/chat.py

@@ -30,10 +30,11 @@ class ChatAgent:
     max_rounds: int
     temperature: float | None
     on_limit: LimitContinueHook | None
+    stream: bool
     messages: list[AnyChatMessage]
     pending_retry_text: str | None
 
-    def __init__(  # noqa: PLR0913
+    def __init__(
         self,
         client: ChatClient,
         *,