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/config/schema.py

@@ -18,6 +18,7 @@ class ChannelsConfig(Base):
 
     Built-in and plugin channel configs are stored as extra fields (dicts).
     Each channel parses its own config in __init__.
+    Per-channel "streaming": true enables streaming output (requires send_delta impl).
     """
 
     model_config = ConfigDict(extra="allow")