feat: create pixel

[MessiasLima]

No description provided.

[gemini-code-assist]

Code Review

This pull request implements the tracking pixel creation endpoint (createPixel) along with its documentation and tests. It also introduces reusable test fixtures for Pixel, Team, TeamMember, and User models to replace inline object literals in tests, aligning with the project's testing guidelines. The review feedback suggests several improvements to these fixtures, such as defaulting deletedAt to null to represent active entities by default, and dynamically linking IDs between parent and nested fixtures (e.g., matching teamId and userId in Team and TeamMember fixtures) to ensure data consistency.

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