fix(ai-gateway): map GLM latest alias to Vercel

[chrarnoldus]

Summary

• register ~z-ai/glm-latest as a managed latest-model alias
• map the alias to the current Vercel GLM model ID, zai/glm-5.3
• cover the mapping and alias catalog in the existing table-driven tests

Testing

• CI only, as requested

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• apps/web/src/lib/ai-gateway/latest-model-aliases.ts
• apps/web/src/lib/ai-gateway/providers/vercel/mapModelIdToVercel.test.ts
• apps/web/src/lib/ai-gateway/providers/vercel/mapModelIdToVercel.ts
• apps/web/src/lib/ai-gateway/providers/zai.ts

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