Replace PNG feature icons with token icons

[BleedingDev]

Feature blocks on the N1 homepage use PNG icons from apps/n1/src/assets/icons/*.png (imported via apps/n1/src/data/home/index.ts / FeatureBlock).

Replace these with token/Icon-based assets (design-system icons) and remove PNG usage. This was intentionally deferred from the PR #197 cleanup.

[BleedingDev]

There are many reasons for this - one of them is scaling. I would understand that we have to keep this in case of more complex icons, that can't be converted into SVG, otherwise we should use SVG via Iconify (should support custom SVGs).