fix(ui): stabilize update animations

[optiplex331]

Summary

• keep update and audit loading icons as the existing RefreshCw arrow animation
• center the SVG rotation to avoid visual overlap or offset while spinning
• keep quick loading states visible briefly so fast checks still show feedback

Root cause

Fast update/audit requests could flip loading state back before the browser painted the spinner, and RefreshCw icons were relying on the default transform origin. Settings also used a different Loader2 icon for update checks, making the animation inconsistent.

Validation

• npx biome check src/pages/settings.tsx src/pages/audit.tsx src/pages/extensions.tsx src/pages/overview.tsx src/stores/audit-store.ts src/stores/extension-store.ts src/stores/update-store.ts src/stores/web-update-store.ts
• npm run build
• git diff --cached --check
• verified Audit and Settings loading states in the in-app browser

Screenshot

• Before:

• After: