Make snap area config export deterministic

[arhxam]

Summary

• serialize snap-area dictionaries in a stable Directional.rawValue order
• preserve Rectangle's existing alternating key/value JSON schema
• canonicalize previously persisted valid snap-area JSON during config export
• preserve raw export behavior for unset, malformed, and unrelated JSON defaults

Fixes #1468.

Verification

• JSONDefaultSerializationTests: 5/5 passing
• full RectangleTests: 210 tests run; the same 22 pre-existing assertions fail as on main, confined to ActiveSideSplitRatiosCooperativeTests, CooperativeCornerResizeTests, and HalfSplitCornerCalculationTests
• git diff --check origin/main...HEAD

AI assistance

AI tooling assisted with investigation, implementation, and test generation. The final diff was reviewed against the issue, independently code-reviewed twice, and verified locally.