feat(routes-f): multi-asset tip support

[davedumto]

Summary

Return supported tipping assets and live USD-equivalent rates.

Requirements

• GET returns { assets: [{ symbol: XLM|USDC|BTC|ETH, usd_rate, min_tip }] }
• Bundle static rates inside folder (mark as test data)
• POST /convert { amount, from, to } returns converted amount
• Tests verify conversion math

Scope Constraint - READ BEFORE STARTING

All files for this task must live inside app/api/routes-f/. This includes the route handler, helpers/utilities, types, and tests. Do NOT modify, import from, or add files to lib/, utils/, types/, components/, or anywhere else outside app/api/routes-f/. If you need shared logic, duplicate it inside your subfolder. Keeping everything scoped to this folder is intentional - it keeps these tasks independent and mergeable in any order.

Product Context

StreamFi is a blockchain-powered live streaming platform. Streamers broadcast via Mux, viewers tip in Stellar XLM/USDC, creators have stream privacy modes (public/unlisted/subscribers-only). Build these issues as practice implementations - use realistic data shapes that match the platform domain, but do not import from the real app code.

[samjay8]

@samjay8 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Boss, please kindly assign this task to me. ETA: 3 hours.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @samjay8 to this issue.

[k-deejah]

@k-deejah has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi Maintainer, I can work on this issue

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

[drips-wave]

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

🧑‍💻 @k-deejah: 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.

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