Add `partio clean` command to remove stale session state

[jcleira]

Summary

Add a partio clean command that removes orphaned and stale state files from .partio/state/. When git hooks are interrupted (crash during commit, failed amend, aborted operations), pre-commit state files can be left behind. Over time these accumulate and can cause spurious checkpoint creation on the next commit.

Default behavior:

• Remove pre-commit state files left by interrupted hook operations
• Remove session state for sessions that ended but whose state files were not cleaned up

With --all flag:

• Remove all session state files regardless of session status

Why

Partio saves detection state to .partio/state/pre-commit.json before each commit and deletes it in post-commit. If the commit is interrupted before post-commit runs, this file lingers. On the next commit, Partio may pick up the stale state and create an incorrect checkpoint linkage. A partio clean command lets users recover without running partio disable && partio enable.

Source

Inspired by entireio/cli PR #846 which fixed entire clean --all to clean all sessions (not just orphaned ones) — changelog 0.5.3.

Acceptance Criteria

• partio clean removes orphaned state files from .partio/state/
• partio clean --all removes all session state files, including idle sessions
• Command is idempotent — safe to run when nothing needs cleaning, exits 0
• Command prints a summary of what was removed (or 'nothing to clean')
• Existing active session state is preserved by default

Program file