PrivatePath CLI Helper

[tony]

Why

• Repeated contract_user_home usage caused inconsistent tilde-collapsing
  and risked leaking $HOME across CLI commands and tests.
• We need a single helper that automatically redacts the home directory when
  rendering paths but otherwise behaves like pathlib.Path.

What

1. Add vcspull._internal.private_path.PrivatePath, a pathlib.Path subclass
   whose str()/repr() collapse the current user's home directory.
2. Replace every CLI and logging call site that previously relied on
   contract_user_home (or raw paths) so human output and JSON/NDJSON schemas
   now consistently use PrivatePath.
3. Remove the legacy helper from vcspull.util and update tests plus log
   snapshots to expect the new behavior; add a dedicated test module for the
   path class.
4. Document the helper in both CHANGES (v1.47.x Development section) and the
   Sphinx internals docs with usage guidelines and an automodule reference.

Testing

• Not run (docs + refactor touches only)

[codecov]

Codecov Report

❌ Patch coverage is 74.00000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.95%. Comparing base (6e27b7d) to head (4580004).
⚠️ Report is 13 commits behind head on master.

Files with missing lines	Patch %	Lines
src/vcspull/cli/add.py	41.66%	7 Missing ⚠️
src/vcspull/_internal/private_path.py	92.30%	1 Missing and 1 partial ⚠️
src/vcspull/cli/discover.py	50.00%	2 Missing ⚠️
src/vcspull/cli/fmt.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
+ Coverage   77.84%   77.95%   +0.11%     
==========================================
  Files          13       14       +1     
  Lines        1882     1901      +19     
  Branches      398      401       +3     
==========================================
+ Hits         1465     1482      +17     
- Misses        271      272       +1     
- Partials      146      147       +1     

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