feat: Indigo theme updates for frontend-base

[arbirali]

Description

This PR updates the Indigo theme to align with the new styling mechanism introduced in openedx/frontend-base.

Previously, styling in MFEs relied on build-time CSS imports. However, with the introduction of runtime configuration in frontend-base, global styles (including Paragon and theme overrides) are now injected dynamically into the document via PARAGON_THEME_URLS.

This change ensures that Indigo correctly provides its theme styles using the runtime configuration approach, allowing consistent branding across all MFEs without requiring rebuilds.

There is a related PR in the brand-openedx #58

How Has This Been Tested

• Verified that PARAGON_THEME_URLS is correctly populated via Tutor configuration.
• Confirmed that CSS files are injected into the at runtime.
• Validated that Indigo branding styles are applied across MFEs (e.g., Learner Dashboard).
• Tested in a dev Tutor environment with MFEs enabled.

Learner Dashboard

Before	After

Authn

Before	After

Profile