feat: add price alert integration tests

[Stanley-Owoh]

Summary

Adds an integration test confirming that a price alert does not re-trigger after the threshold has already been crossed once.

Changes

• New test file: src/modules/alerts/__tests__/alert-no-retrigger-after-threshold.integration.test.ts

What the test covers

1. Creates a price alert with threshold 500 (direction: above)
2. First price update (400 → 600) crosses the threshold — asserts the delivery webhook is enqueued exactly once
3. Asserts the alert record is marked as triggered (isActive: false, triggeredAt set)
4. Second price update (600 → 700) remains above threshold — asserts no additional delivery is enqueued and no additional update is made to the alert record

Acceptance Criteria

• Delivery job enqueued exactly once on first threshold crossing
• No second job enqueued on subsequent above-threshold updates
• Alert record marked triggered after first crossing
• Alert not re-triggered unless explicitly reset

Closes #660

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