Display Settings & Quick Guide:
- Added Display Settings dialog (Settings menu) for chart size, wheel thickness, planet size, planet glyph size, and UI font size
- Added Restore Defaults button to reset all display settings to platform defaults
- Display preferences are now saved to QSettings and restored on next launch
- Added platform-aware defaults with calibrated values for Linux and Windows (125% scaling)
- Added Quick Guide info button in the top-right corner of the main tab widget
- Fixed QLineEdit placeholder text not visible on Windows with the Fusion palette
- Consolidated UI font sizing through global settings and removed NoFontMerging on Windows