[FEATURE]: Add Kiro (kiro.dev) as a selectable provider #26680

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Kiro now supports API-key based authentication for Kiro CLI headless / non-interactive usage via the KIRO_API_KEY environment variable.

OpenCode already supports adding provider credentials through /connect, and it would be useful to have Kiro available as a first-class selectable provider there, instead of requiring custom configuration or third-party plugins.

Requested behavior:

• Add Kiro to the selectable provider list in /connect.
• Support reading credentials from KIRO_API_KEY.
• Optionally allow users to paste a Kiro API key through /connect, similar to other providers.
• Expose supported Kiro models in /models, such as Auto and the models available from Kiro CLI/model metadata.
• Document that Kiro API key authentication is currently for Kiro CLI headless usage and may require a Pro/Pro+/Power subscription and/or admin-enabled API keys.

References:

• Kiro CLI headless mode uses KIRO_API_KEY.
• Kiro API keys can be generated from the Kiro web console for supported plans.
• OpenCode supports adding provider credentials via /connect.