fix(fab): Add dark theme support for FAB Security pages

[shivaam]

Fix dark theme not being applied to FAB Security pages (Users, Roles, etc.)

When dark theme is enabled in the main Airflow UI, the Security menu pages
displayed in light theme because they render in an iframe from the FAB provider.

Root cause:

1. runtime.js was missing from the HTML template - this prevented webpack
   bundles from executing (webpack's runtimeChunk: 'single' config requires
   the runtime to be loaded first)
2. No code was reading the theme preference from localStorage

Changes:

• Add runtime.js to main.html template before other webpack bundles
• Add applyColorScheme() function in main.js to read theme from localStorage
  and set data-color-scheme attribute on document root

Fixes #60541

[boring-cyborg]

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[shivaam]

airflow_ui_bug.mov

Here is a recording using breeze.

[eladkal]

Nice!

[vincbeck]

Really really nice!

[vincbeck]

Static checks are failing

[shivaam]

I have fixed the issue. The problem was that the hashes were not updated for the js changes as I was not able to run pre-commit hook locally earlier. I am able to do it now.

[shivaam]

The compile-fab-assets pre-commit hook is failing in CI due to a hash mismatch between macOS and Linux environments.

Issue:

✅ All checks pass locally on macOS (see screenshot below)
❌ CI fails because it generates a different hash for the same source files
Probable Root Cause: The hash is computed from source files in providers/fab/www/, and differs between macOS

CI Error:

Compile FAB provider assets......................................................Failed

• hook id: compile-fab-assets
• files were modified by this hook

Old hash: e73e02e0b7eafdb1a6d3e8d32d4077bcddf48819650d166b3c40e938ad08a9bc
New hash: 7c7b2ff608159b9ea6048dfdd0dd7ccc0041fd362d54324cc869948585e4cc69
Solution: I've updated providers/fab/www-hash.txt with the CI-generated hash (7c7b2ff608159b9ea6048dfdd0dd7ccc0041fd362d54324cc869948585e4cc69) to match the Linux environment. This should hopefully resolve the static check failure.

Local verification:

Ready for CI approval to verify the fix. 🙏

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.