fix(apps): address functions deployment compatibility and resolve callable signature issues

[josephperrott]

Includes refactored callable return structure and CommonJS deployment stabilizing fixes.

[gemini-code-assist]

Code Review

This pull request significantly improves the application's architecture and security by moving data access to backend callable functions and locking down Firestore. The changes are well-structured and address important deployment compatibility issues. I've found one high-severity issue in the new updateUser function where handling for indefinite blocks is incorrect, which could lead to storing invalid data. A fix is suggested.

[alan-agius4]

This PR was merged into the repository. The changes were merged into the following branches:

• main: 6171abb

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