Add graceful timeout on /api/admin [b#090]

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox FWC26 campaign. Per-request timeout on /api/admin with cooperative abort + 504 on exceed.

Requirements and Context

• Implement per the description above
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented

Suggested Execution

1. Fork the repo and create a branch
2. Implement changes touching:
   • src/routes/admin.ts
   • src/middleware/timeout.ts
3. Test and commit; open a PR with Closes #<issue-number> in the body

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours

[arisu6804]

I would like to work on this issue

[grantfox-oss]

🦊 GrantFox — @arisu6804 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #664)
2. Your PR will be reviewed by the Predictify-org maintainers

Good luck! Track your progress on GrantFox.

[greatest0fallt1me]

Welcome to the GrantFox FWC26 campaign, @arisu6804! You've been assigned. Discord: https://discord.gg/WC53JxDqx