feat: implement labeled slider for clock phase delay control

[darktorres]

Summary

Replaces the previous clock delay spinbox with a custom LabeledSlider widget that displays period fraction values (-1/2 to 1/2) under slider ticks for intuitive phase delay adjustment.

Changes

• Add LabeledSlider custom widget with period fraction label rendering
• Replace DoubleSpinBox with QSlider in ElementEditor UI
• Restrict slider range to -4 to 4 (representing -1/2 to 1/2 period)
• Display labels as fractions: -1/2, -3/8, -1/4, -1/8, 0, 1/8, 1/4, 3/8, 1/2
• Implement backward compatibility by discarding old delay data (< 4.3)
• Fix phase delay direction: negative values advance the clock, positive values delay it
• Update CMakeSources.cmake with new widget files
• Fix include file ordering for code style compliance

Test plan

• Build project successfully with cmake --preset release && cmake --build --preset release
• Run full test suite: ctest --test-dir build
• Verify clock slider displays period fraction labels under ticks
• Test phase delay: negative slider values advance clock, positive values delay clock
• Load files saved with previous versions (< 4.3) to verify backward compatibility
• Verify slider range is restricted to -4 to +4 with no wrapping at extremes

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