Add Herdr to the default bootstrap

[theFong]

Summary

This adds Herdr to the default bootstrap so a new machine gets the terminal workspace manager alongside the other agent tools. If herdr is already on PATH, the bootstrap leaves it alone.

Details

• Uses Herdr's official installer, which detects macOS and Linux architecture, verifies the downloaded binary, and installs to ~/.local/bin.
• Ensures ~/.local/bin is available in the current shell and the user's shell profile.
• Follows the existing installer conventions: record failures without aborting unrelated tools, assert the command is on PATH, and run herdr --version to catch truncated or incompatible binaries.
• Updates the README tool list so the default bootstrap reflects the change.

Validation

• bash -n install.sh
• ./test.sh
• git diff --check