fix(grep): skip .claude/worktrees by default

rtk grep passes --no-ignore-vcs so ripgrep descends into Claude Code's
gitignored .claude/worktrees checkouts, surfacing out-of-scope matches
(worse with --hidden). Add a default rg exclusion glob
(!**/.claude/worktrees/**) matching the directory at any depth, with an
--exclude-dir mirror on the grep fallback. The exclusion is inserted
before user args so a later user --glob can re-include the directory.

Closes #2147

Signed-off-by: Nanook Claw <nanook@agentmail.to>

Author: nanookclaw