Completely added dark mode functionality

[Tapesh-1308]

Description

Added dark mode for every page matching with the UI. Now users can toggle the theme.

• every page made suitable for dark mode commit by committing for your easier understanding
• at last added toggle functionality
• created a theme context, improved settings page UI and enabled it to toggle theme.

Resolves multiple issues people raised: #221 #113 #74 #38

Checklist

Before submitting this pull request, kindly verify that the ensuing checkpoints have been reached.

• [x] Have you adhered to the repository's defined coding convention rules?

Screenshots

Similarly, I have added dark mode for all pages.

Additional Notes/Comments

It took a lot of effort to completely switch to dark mode since there are many pages. Can you please label this PR as level 3😊

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I certify that I have carried out the relevant checks and provided the requisite screenshot for validation by submitting this pull request. I appreciate your contribution.

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[Tapesh-1308]

@hereisSwapnil Can you please quickly review it, as this PR is changing many files and delaying can cause a lot of merge conflicts.