test(cli): add golden coverage for CLI output

[lauritsk]

Problem

Coverage is healthy overall, but src/pid/cli.py has lower coverage and CLI output stability is important for users and docs.

Proposal

Add focused golden/snapshot-style tests for help text, parser errors, status output, runs listings, and config/session commands.

Scope

• In scope:
  • Tests for top-level help/usage paths.
  • Tests for agent/orchestrator error paths.
  • Golden assertions for status/runs output where stable.
  • Keep snapshots readable and low-maintenance.
• Out of scope:
  • Brittle full-terminal styling snapshots unless necessary.

Acceptance criteria

• Key CLI help/error/status paths are covered.
• Tests protect documented output from accidental churn.
• CLI coverage improves meaningfully.
• mise run check passes or exception documented.