feat: sync configured env into task worktrees

[chipssss]

Summary

• Sync a locally configured environment file into newly isolated ship and scout worktrees.
• Refuse unignored targets and keep configured paths and file contents out of output.
• Document the local mapping schema and cover absent mapping, missing source, copying, and ignore enforcement.

Validation

• no-mistakes review, test, and documentation checks passed.
• Local ShellCheck was unavailable; the approved lint exception is recorded here and CI remains the lint backstop.