Harness Worktrees for Pi

Pi-native worktree maintenance for repos that use one git worktree per coding harness.

Mode C: get this worktree current with main

When the user says any of these, treat it as an explicit instruction to make the current worktree match latest origin/main:

• "mode C"
• "get current with me"
• "get this worktree current"
• "reset this worktree to main"
• "refresh this worktree from main"
• "sync this worktree with latest main"
• "after merge, make this worktree current"
• "update this worktree after my PR merged"

Do not only acknowledge. Do not stop at dry-run. Do not ask for another confirmation for a clean worktree, even if the branch is ahead or behind.