Implement Tips Stub API

[aji70]

Task: Implement Tips Stub API

Overview

Monetization beyond subscriptions is unmodeled. A tips stub records intent and amount without real payment processing so frontend tip modals can integrate.

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Goals

• Entity: Tip (fanId, creatorId, amountCents, currency, message?, status: pending|completed|failed, createdAt)
• Endpoints:
  • POST /api/v1/tips — fan tips creator
  • GET /api/v1/creators/me/tips?page&limit — creator inbox
  • GET /api/v1/tips/me — fan history
• Min/max amount validation; audit log on create

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Deliverables

• TipsModule, migration, DTOs, Swagger
• Audit integration
• Unit tests for validation and ownership

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Acceptance Criteria

• Fan cannot tip self (400)
• Tip to non-creator returns 404
• Amount outside range returns 400
• Creator/fan only see their own tip records
• All tips created with status: pending (no real charge)
• At least 8 tests