Stream remote agent replies through micro chat

[asim]

Goal
Make the scaffold -> run -> chat -> inspect loop feel live when micro chat talks to a registered Go Micro agent, not only when it falls back to direct service/tool access. Today micro chat --stream streams provider output for the direct-service path, but the registered-agent path still calls Agent.Chat and prints the final reply after the run completes.

Scope

• Add a streaming registered-agent chat path for micro chat --stream when exactly one target/registered agent is selected.
• Prefer the existing agent/A2A streaming primitives where possible instead of inventing a second protocol.
• Preserve the non-streaming micro chat behavior and the multi-agent router fallback.
• Keep run history/inspect output coherent after a streamed reply.

Acceptance criteria

• A focused CLI/unit test proves micro chat --stream <agent> --prompt ... prints reply chunks before the final completion when a stream-capable agent is available.
• A fallback test proves unsupported streaming still uses the existing Agent.Chat path.
• Documentation/help text explains when --stream applies and how to fall back.
• go build ./..., go test ./..., and golangci-lint run ./... are run or any environment limitation is recorded.