Unify sidebar spacing rhythm

[Lyptik]

Summary

Refine vertical spacing with one shared rule system instead of per-control pixel tweaks.

Spacing rhythm

Each section now defines one base spacing unit and derives:

• normal section top spacing = 1.5× base
• compact spacing = 0.5× base
• normal bottom spacing = 1× base

Top actions

If a section starts with a .panel-actions row (currently Reset camera or Clear data):

• the padding above the action is reduced to 1× base
• the spacing below the action is also exactly 1× base

So those lightweight actions are centered between equal top/bottom breathing room without special rules for Reset/Clear individually.

Advanced end spacing

For a last-child Advanced disclosure:

• folded state ends with compact Advanced padding + normal section bottom spacing
• opened state gives the last Advanced content the same compact padding + normal section bottom spacing

This makes the visual space before the section divider identical whether Advanced is folded or unfolded.

I also reused the same spacing variables for Advanced margin/gaps and the Display field/toggle vertical rhythm.

CSS-only change; no runtime or data behavior changes.