feat: add worktree strategies and branch sanitization

[brosu]

Summary

• add configurable worktree strategies with documented default patterns
• introduce {.branch} and {.branchSafe} template vars (sibling-repo uses safe branch by default)
• add e2e coverage for all strategies and branch/path variants

Testing

• go test ./...
• go run e2e/run.go

[timvw]

Hey @brosu, this is a really nice feature — love the strategy-based approach with the template variables. The set of strategies covers all the common worktree layouts I've seen people use, and the {.branchSafe} vs {.branch} distinction is a thoughtful touch.

Since this was opened, a few PRs landed on main that touch overlapping areas:

• feat: use actual branch name for pr/mr checkout #39 — checkoutPROrMR now looks up the real branch name (replaced getRepoName() usage there)
• feat: ensure upstream tracking for pr/mr worktree branches #40 — added upstream tracking after worktree creation
• chore: add dev-shellenv recipe for running wt from source #41 — added go.work.sum to .gitignore (same change you have here)

The conflicts should be straightforward to resolve — your strategy work is orthogonal to the branch-lookup changes. Would you be up for rebasing onto latest main? Happy to help if you run into any issues.

[timvw]

Thank you @brosu for the excellent implementation! This has been rebased, improved (bug fix in getRepoInfo(), cross-platform E2E tests, docs, shell completions), and merged via #42.

[brosu]

Thank you as well, sorry for not having the time these days to do the rebase myself.
Will try to find a solution for local cross platform testing for future enhancements.