Add ETag / 304 caching on /api/proxy

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox FWC26 campaign (Stellar Wave). Emit strong ETags on /api/proxy and honor If-None-Match with 304 to cut bandwidth on repeat reads.

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:
   • src/routes/proxy.ts
   • src/middleware/etag.ts
3. Test and commit; open a PR with Closes #780 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

[damzempire]

@damzempire has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @damzempire to this issue.

[greatest0fallt1me]

Assigned to @t8849033-wq. Happy building! Discord for questions: https://discord.gg/WC53JxDqx

[drips-wave]

Congratulations, @t8849033-wq! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @t8849033-wq: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊