L1 prerequisite cleanup. Two type-preserving refactors that make
subsequent L1 sub-issues mechanical.
1. Extract getAssetStoredFilename(asset) helper to collapse the
duplicated `isCloud && asset.asset_hash ? asset.asset_hash :
asset.name` branch from useMediaAssetActions (lines 302, 446)
into a single helper. Once BE-933/934 emit file_path and the
cloud spec sync brings it into generated types, only the helper
changes.
2. Add mockFeatureFlags(overrides) test utility under src/test-utils/.
L1 sub-issues will use this consistently instead of re-inventing
the mock shape each time. Includes a FeatureFlags type export
from useFeatureFlags.ts so the mock stays in sync.
Also auto-fixed unrelated tailwind class-order lint errors in four
files (VirtualGrid, RightSidePanel, Textarea, ModelInfoPanel) to
keep CI green.
No behavior change.
