Add zoom‑in and zoom‑out quick buttons on the main toolbar

Is your feature request related to a problem? Please describe. When teachers give lectures in the classroom, we often use touch‑screen classroom computers without a physical keyboard. Currently zoom‑in and zoom‑out are hidden inside sub‑menus, which requires multiple clicks during class. This affects the smoothness of live teaching.

Describe the solution you'd like I hope to add dedicated zoom‑in and zoom‑out shortcut buttons directly on the outermost main toolbar, just like OpenBoard. No need to open nested sub‑menus.

For teachers' daily usage priority: Pen and Move tool are used most frequently, followed by zoom‑in / zoom‑out, then guide lines, and other functions are only used occasionally.

Describe alternatives you've considered Keyboard shortcuts for zoom work, but classroom touch‑screen devices often have no keyboard connected.

Additional context Many educators use Rnote for classroom blackboard‑style teaching. Quick zoom buttons will greatly improve classroom practical experience.