Fix UI Suspense loader fallbacks

[shah-harshit]

Description

Lazy-loaded UI routes and active-tab content do not consistently own an appropriate Suspense fallback. This can cause stacked loaders during tab navigation or leave blocking page and tab transitions without the expected progress feedback.

Expected behavior

• Embedded and background lazy content should remain silent by default.
• Page-level lazy boundaries should show the full-page loader.
• Active-tab lazy boundaries should show one tab-content loader.
• Existing 1.13 component behavior should remain unchanged outside the fallback handling.

Scope

Backport the Suspense loader fallback changes to 1.13, preserve the existing 1.13 implementations, and cover the fallback behavior with focused unit tests.

Tracked by #31827.

[shah-harshit]

Completed by #31827, which adapted source #29746 / main commit 9b4e008d directly onto 1.13 while preserving the existing 1.13 implementations. The PR merged as f759c1065b. The original split tracker open-metadata/openmetadata-collate#4230 has also been updated with the final backport status.