fix(auth): remove password min_length validation from LoginRequest

[Vaishnavi10706]

Description

This PR fixes the login request validation by removing the min_length=8 constraint from the LoginRequest schema.

Previously, login requests with passwords shorter than 8 characters were rejected with a 422 Unprocessable Entity response before reaching the authentication logic. Password complexity rules should only be enforced during account creation, not during login.

Changes Made

• Removed min_length=8 from LoginRequest.password.
• Retained max_length=128 to guard against excessively large inputs.
• Added a regression test to ensure login requests are not rejected by schema validation due to password length.

Related Issue

Fixes #1679

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v (relevant authentication tests) and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Test evidence

pytest backend/tests/test_auth_endpoints.py

============================= test session starts =============================
...
============================= 9 passed in 5.05s =============================

[imDarshanGK]

@Vaishnavi10706

[Vaishnavi10706]

@imDarshanGK I have made this changes . now all checks are passed
whenever you get time please review it and tell me if any other changes are required ?
Thank you