Expand shorthand `margin` and `width` properties for `.section` and
`.brightness-levelbar` to individual longhand properties, likely to
avoid issues with older GTK/CSS parsing.
- Add `einkRefresh()` helper calling `pdlc-cli --refresh` after rotation,
brightness changes, waveform changes, and when the widget opens
- Disable CSS transitions and animations globally to reduce ghosting
- Remove button hover transform and transition effects
- Update README with e-ink-specific guidance and tuning notes