chore: add setup task for worktree local files

[zawakin]

Summary

• Add scripts/open-url.local.sh.example as a committed template for the gitignored local hook
• Add mise run setup task that copies *.example → *.local.sh for all local hooks
• Idempotent: skips files that already exist
• Run once after git worktree add to bootstrap local configuration

Usage

git worktree add ../agtrace-2
cd ../agtrace-2
mise run setup   # Creates scripts/open-url.local.sh from template

Test plan

• mise run setup creates the local file from template
• Running again is a no-op ("Nothing to do")
• CI passes

🤖 Generated with Claude Code

[zawakin]

Superseded by env var approach (OPEN_URL_CMD)