cli(feat[introspection]): Contract $HOME to ~/ in human-readable output

[tony]

why: Displaying full home paths like /home/username exposes usernames and creates unnecessary verbosity in human-readable output. Using ~/ is more concise, privacy-friendly, and portable across systems.

what:

• Add contract_user_home() utility function in util.py
• Apply path contraction in list command human output
• Apply path contraction in status command human output
• Apply path contraction in sync dry-run plan output
• Preserve full paths in JSON/NDJSON output for machine consumption
• Update docs to show ~/ in human-readable examples
• Add 3 comprehensive tests for contract_user_home()

Examples:
Before: • tiktoken → /home/d/study/ai/tiktoken After: • tiktoken → ~/study/ai/tiktoken

JSON output still shows full paths for automation: {"path": "/home/d/study/ai/tiktoken", ...}

tests: 195/195 passing (3 new tests added)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.33%. Comparing base (53974f1) to head (ece928a).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #473      +/-   ##
==========================================
+ Coverage   79.15%   79.33%   +0.18%     
==========================================
  Files          14       14              
  Lines        1439     1452      +13     
  Branches      309      311       +2     
==========================================
+ Hits         1139     1152      +13     
  Misses        185      185              
  Partials      115      115              

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