fix(web): hide decorative avatars from screen readers

[thomasorgeval]

Summary

• Mark app icons and generated initials as decorative when the same app/member name is already rendered as nearby text.
• Use empty alt text for repeated app icon images in selectors and Review cards.

Expected impact

• Reduces duplicate announcements for screen reader users in app filters, Reply Inbox cards, and Organization member rows.
• Keeps the existing visual treatment unchanged.

Verification

• pnpm format:check
• pnpm lint
• pnpm nx typecheck web --tui=false