Improve ShouldSync return type

[jonburdo]

This changes ShouldSync to return a Reason type instead of three separate values.

🤖 Generated with Claude Code

fixes #82

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.66667% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.56%. Comparing base (0b6d3e5) to head (cf85c29).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/sync/manager.go	90.90%	3 Missing ⚠️
internal/sync/mocks/mock_manager.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
+ Coverage   65.25%   65.56%   +0.31%     
==========================================
  Files          58       58              
  Lines        3589     3613      +24     
==========================================
+ Hits         2342     2369      +27     
+ Misses       1090     1088       -2     
+ Partials      157      156       -1     

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[jonburdo]

This is based on comment #77 (comment)

@blkt Was this roughly what you had in mind? I'm happy to use a different approach if not. This seemed like the simplest, but we could keep reason's as string constants or use a struct like Decision{ShouldSync: false, Reason: "sync-already-in-progress"}

[dmartinol]

Thanks!