Add copy-ignored and .worktreeinclude patterns for Codex-friendly worktree bootstrapping

[adrianmross]

Problem

Fresh worktrees often need ignored files or directories such as .env, caches, or dependency state. The plugin currently does not surface WorkTrunk's wt step copy-ignored workflow or .worktreeinclude patterns.

Proposal

• Add docs for wt step copy-ignored in post-start / post-create flows
• Add example .worktreeinclude patterns
• Include repo examples for common JavaScript / pnpm / direnv setups
• Add a command doc that helps users apply the pattern intentionally instead of ad hoc copying

Why

This is one of the highest-leverage WorkTrunk patterns for reducing cold-start pain in new worktrees.