Fix/deepseek flash vision

[sebowang]

Summary

What does this PR do and why?

Scope of changes

• Backend (Python / FastAPI)
• Frontend (React / Vite)
• iOS app
• watchOS app
• Agent prompts or tools
• Messaging gateways
• Docs / tests / tooling only

Testing

How did you verify the change works? Include commands, steps, or screenshots.

• python -m pytest tests/ -x -q passes
• npm run build passes (if frontend touched)
• Manual smoke test on at least one entry point (chat / cron / iOS quick check)

Checklist

• No secrets, tokens, API keys, or personal data committed
• No Chinese characters in code, tests, or committed docs
• New user-facing strings are added to i18n locale files (frontend en.json/zh.json, backend backend/i18n/locales/, iOS Localizable.xcstrings)
• New env vars are documented in .env.example
• New features respect the three Agent Design Principles in AGENTS.md
• By submitting this PR I agree to license my contribution under the project's PolyForm Noncommercial License 1.0.0