WebUI-created worktrees are locked at creation by the agent
(cli._setup_worktree locks with --reason 'hermes pid=...'), but
remove_worktree_for_session never unlocked, so git refused every removal
with "use 'remove -f -f' to override or unlock first" — force=true
included, since a single --force cannot override a lock.
Mirror the agent's own _cleanup_worktree ordering: fail-soft
'git worktree unlock' right before the remove, after all
dirty/untracked/unpushed/stream/terminal guards have passed. Those
guards remain the real safety layer; force keeps meaning 'override
dirty working state', never 'override a foreign lock'.
Tests: locked worktree now removes cleanly without force; unlock is
fail-soft when the worktree was never locked; existing mocked
call-order assertions updated for the leading unlock call.
Fixes#6023