fix: disable Tencent Hy3 free model

[chrarnoldus]

Summary

• Disable tencent/hy3:free, excluding it from Auto Free routing and preferred models.
• Mark the free model unavailable for stale clients without disabling paid tencent/hy3.
• Update regression coverage and use an active free model for the rate-limiting test.

Verification

• Passed: formatting, targeted oxlint on all six changed files, and git diff --check.
• Local pnpm --filter web typecheck exceeded the two-minute environment limit during the tRPC build; CI will verify types.
• Tests intentionally delegated to CI as requested.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Disabling tencent/hy3:free via exclusive status and the unavailable-model list follows existing patterns and leaves paid tencent/hy3 intact.

Files Reviewed (6 files)

• apps/web/src/app/api/openrouter/[...path]/route.test.ts
• apps/web/src/lib/ai-gateway/models.test.ts
• apps/web/src/lib/ai-gateway/providers/tencent.ts
• apps/web/src/lib/ai-gateway/unavailable-models.test.ts
• apps/web/src/lib/ai-gateway/unavailable-models.ts
• apps/web/src/tests/openrouter-models-config.test.ts

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_{Reviewed by grok-4.6 · Input: 189.9K · Output: 9.9K · Cached: 393.2K}

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