fix hook-managed worktree routing

[sven1103-agent]

Summary

• mutate hook payloads in place so worktree path rewrites and slash-command normalization work with the current OpenCode runtime contract instead of relying on replaced output.args or output.parts
• handle remotes with unknown or missing default branches more safely, including empty repositories with no remote base branch yet, and add regression coverage for the CLI and hook behavior
• document the validated runtime boundary and update the worktree routing plan so hard guarantees are reserved for plugin-controlled mutating tool paths

Testing

• node --test test/hook-enforcement.test.js test/plugin-entrypoint.test.js test/base-branch.test.js test/cli.test.js

Related

• Fixes Plugin loads, but write flow is not redirected into prepared worktree #62
• References Handle empty repositories when remote HEAD/default branch is unknown #65