Create util.ExecWithOutput and util.ExecRun to consolidate repeated
exec.Command patterns across witness/handlers.go and refinery/manager.go.
Changes:
- Add internal/util/exec.go with ExecWithOutput (returns stdout) and
ExecRun (runs command without output)
- Refactor witness/handlers.go to use utility functions (7 call sites)
- Refactor refinery/manager.go, removing unused gitRun/gitOutput methods
- Add comprehensive tests in exec_test.go
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
