feat(config): add GLM-5.1 and GLM-5V-Turbo to GLM preset models

[wyuc]

Summary

• Add GLM-5.1 and GLM-5V-Turbo to the GLM provider preset model list in lib/ai/providers.ts
• GLM-5.1: 200K context, 128K output, text-only reasoning model
• GLM-5V-Turbo: 200K context, 128K output, vision-enabled multimodal model

Closes #436

Type of Change

• New feature (non-breaking change that adds functionality)

Evidence

• CI passes (pnpm check && pnpm lint && npx tsc --noEmit)
• Manually tested locally

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• My changes do not introduce new warnings

[cosarah]

LGTM