feat: add lightweight empty-state illustration assets

[kike-alt]

Closes #251

Summary

• add lightweight vector illustration assets in mobile/assets/illustrations
• map illustration types in mobile/components/ui/Illustration.tsx to reusable visual assets
• update mobile/components/ui/EmptyState.tsx to render mapped illustrations consistently

Testing

• npm test -- --watchman=false: pass
• npm run lint: fails with pre-existing repo-wide lint issues
• npm run build (repo root): fails because shared workspace build cannot find tsc (pre-existing environment/dependency setup issue)

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