Make logarithmic frequency-axis labels readable at different window sizes #12

Goal

The screenshot shows crowded frequency ticks, especially in the low-frequency region. Improve label readability without changing DSP.

Acceptance criteria

• Reduce overlapping labels while preserving useful log-frequency grid lines.
• Use consistent, understandable Hz/kHz units.
• Check both spectrum and correction plots at small and large window sizes.
• Preserve plot zoom/pan behaviour.
• Include before/after screenshots in the pull request.

Starting points

Window.plot in src/omazone/gui.py; pyqtgraph axis tick configuration. No audio expertise is required for this task. Avoid tests that merely repeat the implementation; visual checks at representative sizes are appropriate.