Fix: Make login screen responsive by using height value from UiSizes

[bhawesh2002]

Description

Problem: Bottom overflowed error when user is on login screen.

Preview of the problem:

Reason: Hard Coded value of height=780 is used for setting height(line 38 of login_screen.dart) of the Container containing login screen elements

Fix: Set height=UiSizes.height_780 to implement responsive design instead of using hard coded values

Fixes

287 : Bug:- Bottom overflowed error on login screen

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Refactor (does not change functionality, e.g. code style improvements, linting)

  How Has This Been Tested?

The changes are tested on Android Emulator (API 33: Pixel 8 Pro) and on Moto g40 Fusion(API 32). The changes fixes the bug without raising any additional errors

Preview After Fix:

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings

Maintainer Checklist

• [x] closes #287 (Replace xxxx with the GitHub issue number)
• [x] Tag the PR with the appropriate labels

[AyaNady17]

Good Work @bhawesh2002 🚀

This is good to merge will merge after the previously scheduled PR's are merged