API docs: `/proposals/summarise` endpoint

[codebestia]

Write apps/ai_agent/docs/api-proposals-summarise.md documenting POST /proposals/summarise — request shape, the three risk levels, and fallback behavior for invalid/missing risk values.

Acceptance criteria:

• Request and response fields are documented with types and every valid risk-level value
• The empty-summary error case (502, per the existing test suite) is documented with its exact response shape
• A worked example is included for each of the three risk levels

[martinshub-tech]

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

I'd like to take this issue. I've analyzed the root cause and am confident I can deliver a reliable fix with proper testing

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

[ChuyCode15]

@ChuyCode15 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi 👋 I'd like to take on this issue. I am committed to delivering a robust, production-grade implementation that adheres to strict clean code principles, separation of concerns, and comprehensive testing. I will invest the necessary time to ensure the solution is efficient and reliable, staying aligned with the estimated timeframe without cutting corners. Could you assign it to me? Thanks!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ChuyCode15 to this issue.

[drips-wave]

Congratulations, @ChuyCode15! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @ChuyCode15: 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 🌊