Add integration test for price alert registration returning 409 for duplicate alert

[Chucks1093]

Summary

A wallet should not be able to register two active alerts for the same creator, direction, and target price. Submitting a duplicate should return 409 with a clear error rather than silently creating a second alert that fires twice.

Scope

• Register a price alert for a creator with a specific direction and target price
• Register the same alert again with identical fields
• Assert the second registration returns 409
• Assert only one alert record exists in the database

Acceptance Criteria

• Second identical registration returns 409
• Error body explains that an identical alert already exists
• Only one alert record in the database after both requests

ETA: 12 hours

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Coordinate on Telegram

[Oluwasuyi-Timilehin]

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

Hello, please assign this to me. I would get started immediately

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[parkerwinner]

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

Hi, am familiar with server issues and can resolve this issue robustly, kindly assign it to me

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