🎨 Palette: Add missing ARIA labels to admin icon buttons

[Woschj]

This PR implements missing ARIA labels for icon-only action buttons across the core admin dashboard interfaces (departments.html, software_management.html, and users.html).

These changes improve screen reader compatibility without altering the visual design or backend logic, adhering strictly to the UX standards and Palette's 50-line PR constraint.

Changes

• Departments View: Added aria-label="Abteilung umbenennen" and aria-label="Abteilung löschen" to rename/delete buttons.
• Software Management: Added aria-label="Software löschen", aria-label="Nutzergruppe bearbeiten", and aria-label="Nutzergruppe löschen".
• Users View: Added aria-label="Benutzer löschen" to the recycle bin action.

All test suites and linters pass without new regressions.

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PR created automatically by Jules for task 4646783135000497678 started by @Woschj

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