[TASK] git worktree list --porcelain parsing

[kirich1409]

Context

Parse porcelain format fields: HEAD, branch, bare, detached, locked, prunable.

Acceptance criteria

• Parser round-trips all fields.
• Unit tests cover edge cases (bare, locked, prunable).

Files to touch (estimate)

best-effort estimate; agent refines during implementation

Implementation notes

n/a

Dependencies

• Blocked by [TASK] CommandRunner protocol + CommandRunnerImpl with allowlist #39

Safety checklist

See .github/ISSUE_TEMPLATE/task.yml — tick applicable invariants in the issue if any destructive path is touched.

Definition of Done

• Acceptance criteria satisfied and verifiable
• Tests added or updated
• No build / lint / test regressions
• Self-review against research-report invariants
• Code review approved