fix: additional user api leaks

[andypols]

Summary

This PR builds on #1090 by ensuring consistency in how user data is serialised and returned across multiple authentication-related endpoints.

Changes

The following endpoints now return user data using the same public-facing serialisation object introduced in PR #1090:

• POST /auth/login — returns the user upon successful login
• GET /auth/profile — returns the authenticated user
• GET /auth/me — returns the authenticated user

I Introduced a new loginSuccessHandler function to encapsulate the login success logic. This allows for easier unit testing of login behavior independently of Passport's internal flow.

Note: /auth/profile and /auth/me currently serve the same purpose and return identical responses. Consolidating or removing one of these is a potential cleanup task, but is out of scope for this PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.40%. Comparing base (4956b73) to head (40df0d1).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/service/routes/auth.js	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1098      +/-   ##
==========================================
- Coverage   77.40%   77.40%   -0.01%     
==========================================
  Files          55       56       +1     
  Lines        2293     2288       -5     
  Branches      258      258              
==========================================
- Hits         1775     1771       -4     
+ Misses        488      487       -1     
  Partials       30       30              

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[jescalada]

LGTM! 🚀

A bit of manual testing to confirm: