feat(macos): prefer tabs over new Finder windows

[shunk031]

Motivation

Prefer tabs when macOS or Finder would otherwise open a new window.

Changes

• Set AppleWindowTabbingMode to always systemwide.
• Set Finder's FinderSpawnTab preference so folders open in tabs.
• Document the behavior in the shell function description.

Testing

• make setup completed before this change.
• git diff --check passed.
• Repository commit hooks passed.
• No local macOS runtime test was run; GitHub Actions and Codecov checks all passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.90%. Comparing base (58fcdfe) to head (0f15a88).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #773      +/-   ##
==========================================
+ Coverage   80.86%   80.90%   +0.03%     
==========================================
  Files          25       25              
  Lines        1113     1110       -3     
==========================================
- Hits          900      898       -2     
+ Misses        213      212       -1     

Flag	Coverage Δ
macos	41.66% <ø> (ø)
rockylinux	80.88% <ø> (-0.10%)	⬇️
ubuntu	80.02% <ø> (+1.15%)	⬆️

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