#8 a11y: add semantics labels to icon-only buttons

[Anonymous]

Originally created by: Caqil

Icon-only controls (e.g. AppIconButton usages in the home header) can be unlabeled for screen readers.

• Audit icon-only buttons for a missing Semantics/tooltip/semanticLabel
• Add localized labels (keys in assets/translations/)

Pick one screen to keep the PR small. See ARCHITECTURE.md for where the UI lives.