[Feat] Add OpenCode CLI as a provider

[patricka3125]

Overview

Add OpenCode CLI (more precisely TUI) as a provider
https://opencode.ai/docs/tui/

User Stories

• Empowers the user with the option to use CLI backed with a broad amount (75+) model providers (with Ollama support for self-hosting).
• As of today, Opencode project currently has ~142K Github stars (https://github.com/anomalyco/opencode)

Acceptance Criteria

• OpenCode provider is fully implemented, all CAO features today function without regression

Proposed solution

• Follow the recently introduced cao-provider skill to steer implementation.

[haofeif]

@patricka3125 sounds good to me. Please refer to the https://github.com/awslabs/cli-agent-orchestrator/tree/main/skills/cao-provider for development.