test(ci): cover Windows and Git Bash so #112 cannot regress

[timvw]

The Git Bash bug in #112 shipped because nothing ran there: unit tests were Linux-only, and the Windows E2E legs only ran PowerShell and pwsh. Git Bash runs the same native wt.exe as PowerShell but through the bash integration — a combination no job covered.

CI coverage

• Unit test job becomes a matrix: ubuntu-latest + windows-latest. No -race on the Windows leg (it needs a cgo toolchain, and the point is running the suite on a Windows host); coverage is still uploaded from Linux only.
• New E2E leg: windows-latest × bash. e2e/run.go resolves bash from the Git for Windows install rather than PATH, so the WSL launcher in System32 is never picked up; exports MSYSTEM (a bash -c does not read /etc/profile); and translates paths with cygpath, since the interpreter only understands POSIX paths while wt.exe only understands native ones.

Regression scenarios

Windows-only (skip_os: [linux, darwin]), one per symptom of #112:

• wt init --dry-run under Git Bash must emit eval "$(wt shellenv bash)" and not Invoke-Expression.
• wt shellenv with no args must emit the bash wrapper, not PowerShell code.

The existing checkout_auto_cd_verified scenario now also runs on Git Bash, which is the literal symptom reported in the issue.

Unit tests

cmd/shellenv_wrapper_test.go executes the generated bash wrapper against a fake wt on PATH, covering:

• the missing-script(1) fallback — auto-cd still works, redirected output is replayed, and the command's exit status survives rather than tee's;
• cygpath translation of native Windows paths.

Both branches are driven from an ordinary bash by controlling what the wrapper's command -v probes find, so they run on every OS rather than only on Windows. Reverting either half of the #112 fix makes them fail.

Refs #112

[codecov]

Codecov Report

❌ Patch coverage is 4.87805% with 39 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.91%. Comparing base (90726cb) to head (4bf8308).

Files with missing lines	Patch %	Lines
e2e/run.go	0.00%	39 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #114      +/-   ##
==========================================
+ Coverage   32.22%   36.91%   +4.68%     
==========================================
  Files          27       27              
  Lines        3066     3102      +36     
==========================================
+ Hits          988     1145     +157     
+ Misses       1993     1871     -122     
- Partials       85       86       +1     

Files with missing lines	Coverage Δ
cmd/worktree_path.go	58.53% <100.00%> (+0.25%)	⬆️
e2e/run.go	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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