Handle worktree paths with spaces in /clean_gone

[fallintoplace]

What this does

Updates /clean_gone to discover gone branches with git for-each-ref and parse linked worktrees with git worktree list --porcelain -z.

The current command reads the column-oriented worktree output with awk. For a linked worktree at /tmp/my project/feature, it resolves only /tmp/my, so removal fails and the branch remains checked out. The $1 expression in awk is also interpreted as a positional command argument before the shell command runs.

Using the structured formats keeps branch matching exact and preserves complete worktree paths.

How we know it works

• Ran the exact command against a repository containing both a regular gone branch and a linked worktree at a path with spaces.
• Verified the linked branch feature/test.v1 and its worktree were removed.
• Verified the regular gone branch was removed and main was preserved.
• Checked the embedded command with bash -n.
• Ran git diff --check.