feat(byok): add OpenCode Go provider

[chrarnoldus]

Summary

• Add OpenCode Go as a direct user BYOK provider at https://opencode.ai/zen/go/v1.
• Synchronize its model catalog from models.dev and recommend Qwen3.7 Plus as the resilient fallback model.
• Prefer Anthropic Messages for MiniMax and Qwen models while retaining OpenAI-compatible Chat Completions for other model families.

Verification

Not performed before PR creation, per requested sequencing.

Visual Changes

N/A

Reviewer Notes

The direct BYOK provider contract now supports an optional per-model AI SDK provider override so OpenCode Go can select Anthropic Messages only for MiniMax and Qwen models.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

The incremental commit (refactor(byok): colocate OpenCode Go model detection) is a clean colocation refactor — isOpenCodeGoMessagesModel is moved from model-settings.ts into opencode-go.ts where it logically belongs, and the test import is updated accordingly. The .toLowerCase() normalization was dropped, but this is safe since model IDs sourced from models.dev sync are always lowercase, and the provider prefix 'opencode-go' is a known lowercase constant throughout the codebase.

Files Reviewed (3 files, incremental)

• apps/web/src/lib/ai-gateway/providers/direct-byok/opencode-go.ts
• apps/web/src/lib/ai-gateway/providers/direct-byok/opencode-go.test.ts
• apps/web/src/lib/ai-gateway/providers/model-settings.ts

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_{Reviewed by claude-4.6-sonnet-20260217 · 256,312 tokens}

_{Review guidance: REVIEW.md from base branch main}