Request: enable PR submission for DeepSeek model update

[Zzy-min]

DeepSeek API model update

I found that the current built-in DeepSeek configuration still sends deepseek-chat for every AI polish and grammar request. DeepSeek now rejects that retired model identifier and accepts deepseek-v4-flash or deepseek-v4-pro.

I prepared and verified the minimal fix:

• change src/config/ai.ts: deepseek-chat -> deepseek-v4-flash
• validation: pnpm build passed
• fork branch: https://github.com/Zzy-min/magic-resume/tree/agent/fix-deepseek-v4-model
• compare: https://github.com/JOYCEQL/magic-resume/compare/main...Zzy-min:magic-resume:agent/fix-deepseek-v4-model?expand=1

The repository currently restricts both Issue and PR creation for my account, so GitHub rejected the PR request. Could you please enable external PR submissions for this repository, or invite Zzy-min as a collaborator so I can submit this one-line fix for review?