feat(ui): add global styles and support for dark mode

[purnimagarg1]

Linear ticket:
https://linear.app/acryl-data/issue/CAT-1770/add-global-styles-and-support-for-dark-mode

[github-actions]

Linear: CAT-1772

[codecov]

Bundle Report

Changes will increase total bundle size by 21.19kB (0.09%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
datahub-react-web-esm	22.75MB	21.19kB (0.09%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: datahub-react-web-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/index-*.js	21.19kB	12.5MB	0.17%

Files in assets/index-*.js:

• ./src/app/useSetAppTheme.tsx → Total Size: 1.82kB

• ./src/CustomThemeProvider.tsx → Total Size: 676 bytes

• ./src/app/theme/useIsDarkMode.ts → Total Size: 1.13kB

• ./src/app/theme/GlobalThemeStyles.tsx → Total Size: 19.41kB

[alwaysmeticulous]

🔴 Meticulous spotted visual differences in 777 of 1446 screens tested: view and approve differences detected.

Meticulous evaluated ~9 hours of user flows against your PR.

_{Last updated for commit 81f776d Merge branch 'master' into pg--cat-1770-dark-mode-support. This comment will update as new commits are pushed.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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