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
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