feat(shell): Add shell run summary policy and mute flag

[EspenAlbert]

Summary

• Adds ShellRunSummary (all / errors_only) on AskShellSettings, env ASK_SHELL_SHELL_RUN_SUMMARY.
• Skips per-command completion logs in rich_run_state.remove_run when summary is errors_only and the run exited zero.
• Adds ShellConfig.mute_shell_summary to skip completion logs for a single run (probes).
• log_task_done logs expected non-zero exits (allow_non_zero_exit) at warning instead of error.
• run and run_and_wait accept mute_shell_summary.
• Tests cover summary policy and mute; conftest mocked ShellConfig includes new fields.

Notes

• Default remains all for backward compatibility. tfdo sets errors_only via env after its CLI callback.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.56%. Comparing base (dfbbfc3) to head (22f984d).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
+ Coverage   85.43%   85.56%   +0.13%     
==========================================
  Files          20       20              
  Lines        1860     1878      +18     
==========================================
+ Hits         1589     1607      +18     
  Misses        271      271              

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