feat(app): support custom max_active_requests per app

[qiaofenlin]

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Summary

This PR adds support for customizing the maximum number of concurrent active requests (max_active_requests) per app.

• Users can now set this value in the app edit modal on the frontend.
• The field and its tooltips are fully internationalized (English & Chinese).
• i18n text is improved to clarify that 0 means unlimited.

Motivation:
Allows app owners to control resource usage and prevent overload by limiting concurrent requests per app.

Dependencies:
No new dependencies.

Fixes #22098

Screenshots

Before	After

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

It seems the gap between the input and description isn't correct.

[qiaofenlin]

It seems the gap between the input and description isn't correct.输入和描述之间的差距似乎不正确。

@crazywoola Thank you for your review and feedback!
Previously, I used "最大并发数" because I thought it would be easier for users to understand. However, after reconsidering your comments, I realized that this translation was not accurate enough. I have now updated the translation as shown in the screenshot below.
If there are still any issues or suggestions, please feel free to discuss them with me. I am happy to make further improvements!

[crazywoola]

[qiaofenlin]

@crazywoola Thank you very much for your feedback!
Previously, I misunderstood the requirement, which led to an incorrect modification last time.
Now, I have adjusted the styles as requested. Could you please review it again?
If there are still any issues, feel free to let me know—I’ll do my best to support and fix them.
The updated screenshots are as follows:

[qiaofenlin]

Hi @crazywoola

I have addressed the review suggestions and pushed the corresponding changes some time ago. I noticed that the review has not been updated for a while, so I wanted to kindly check if there are any remaining concerns or if there’s anything else I should improve.

Please let me know if you need any further information from my side. Thank you for your time and feedback!

Best regards.