fix: Use only shorthand properties for margin and padding

[stravo1]

Summary

• After feat: add 4 corner resize controls and rotation handler #665 a block could end up with more than two margin/padding styles set at once — one shorthand (margin) and separate per-side ones (margin{Position}), which could conflict.
• Spacing is now written and read back using only the shorthand property.

Before:

Screen.Recording.2026-07-24.at.2.30.30.PM.mp4

After:

Screen.Recording.2026-07-24.at.2.58.17.PM.mp4

Fixes: #690

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the change is a focused, well-contained refactor of spacing write/read paths with correct backward-compat handling of legacy longhand data.

Every mutation goes through setSpacingShorthand, which reads the current expanded shorthand, patches only the updated sides, clears longhands, and writes a single collapsed shorthand atomically. Legacy longhand data is honoured at read time via getSpacingParts, and collapseBoxShorthand/expandBoxShorthand round-trip correctly including functional values like calc(). No edge cases were found.

No files require special attention.

_{Reviews (2): Last reviewed commit: "fix: Don't split functional CSS values o..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.88%. Comparing base (d2d3b23) to head (f491428).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #693   +/-   ##
========================================
  Coverage    56.88%   56.88%           
========================================
  Files           35       35           
  Lines         4217     4217           
========================================
  Hits          2399     2399           
  Misses        1818     1818           

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