[FEATURE]: Add Kiro provider to V2 (bundled opencode-kiro plugin) #54536

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

Add Kiro (kiro.dev) as a provider in OpenCode, bundled as a built-in plugin.

The V1 version of this was PR #20491 (bundled opencode-kiro plugin, as requested by a maintainer). It was closed when dev moved to V2 with a request to port it over, and the earlier issues (#9165, #26680) were closed as well, so this tracks the V2 port.

How it works:

• opencode-kiro registers a kiro integration with a "Kiro CLI Login" method that uses the official kiro-cli login (Builder ID, IAM Identity Center, etc.), so auth stays within Kiro's terms.
• The models available come from the ones listed in Models.dev PR doing an intersection with the ones that the user's own kiro-cli lists (the models they actually have access to), with reasoning-effort variants where supported.
• Requests go through kiro-acp-ai-provider, an AI SDK provider that talks to kiro-cli over ACP; core never deals with ACP directly. The SDK is only loaded once the user connects Kiro.
• Kiro is credit-based, so a small TUI plugin shows session credits next to the context info.

The plugin is published for V2 (opencode-kiro) and tested on OpenCode 2.0.26.