feat: add error handling for flagged generation

[monkeyWie]

No description provided.

[augmentcode]

🤖 Augment PR Summary

Summary: Adds explicit handling for Cloudflare “flagged” generation failures so the UI can show a targeted message instead of a generic error.

Changes:

• Introduces new generation failure reasons: PROMPT_FLAGGED and INPUT_IMAGE_FLAGGED (DB schema + UI mapping).
• Adds EN/ZH i18n strings for the new error states.
• Adds GenError and updates the Cloudflare provider to map policy-related 400 responses to these reasons.

Technical Notes: Cloudflare 400 responses are inspected for error code 3030 to classify policy violations.

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[augmentcode]

Review completed. 1 suggestions posted.

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[augmentcode]

On 400 responses, JSON.parse(errorText) (and firstErr.message.includes(...)) can throw if Cloudflare returns non-JSON or the shape differs, which would skip the intended GenError mapping. Consider guarding the parse/message access so flagged requests reliably surface as PROMPT_FLAGGED / INPUT_IMAGE_FLAGGED.

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