feat: add streaming channel support with automatic fallback

Provider layer: add chat_stream / chat_stream_with_retry to all providers
(base fallback, litellm, custom, azure, codex). Refactor shared kwargs
building in each provider.

Channel layer: BaseChannel gains send_delta (no-op) and supports_streaming
(checks config + method override). ChannelManager routes _stream_delta /
_stream_end to send_delta, skips _streamed final messages.

AgentLoop._dispatch builds bus-backed on_stream/on_stream_end callbacks
when _wants_stream metadata is set. Non-streaming path unchanged.

CLI: clean up spinner ANSI workarounds, simplify commands.py flow.
Made-with: Cursor

nanobot/channels/base.py

@@ -76,6 +76,17 @@ class BaseChannel(ABC):
         """
         pass
 
+    async def send_delta(self, chat_id: str, delta: str, metadata: dict[str, Any] | None = None) -> None:
+        """Deliver a streaming text chunk. Override in subclass to enable streaming."""
+        pass
+
+    @property
+    def supports_streaming(self) -> bool:
+        """True when config enables streaming AND this subclass implements send_delta."""
+        cfg = self.config
+        streaming = cfg.get("streaming", False) if isinstance(cfg, dict) else getattr(cfg, "streaming", False)
+        return bool(streaming) and type(self).send_delta is not BaseChannel.send_delta
+
     def is_allowed(self, sender_id: str) -> bool:
         """Check if *sender_id* is permitted.  Empty list → deny all; ``"*"`` → allow all."""
         allow_list = getattr(self.config, "allow_from", [])
@@ -116,13 +127,17 @@ class BaseChannel(ABC):
             )
             return
 
+        meta = metadata or {}
+        if self.supports_streaming:
+            meta = {**meta, "_wants_stream": True}
+
         msg = InboundMessage(
             channel=self.name,
             sender_id=str(sender_id),
             chat_id=str(chat_id),
             content=content,
             media=media or [],
-            metadata=metadata or {},
+            metadata=meta,
             session_key_override=session_key,
         )