Add three layers of protection to prevent accidental branch switches in
the town root (~/gt), which should always stay on main:
1. Doctor check `town-root-branch`: Verifies town root is on main/master.
Fixable via `gt doctor --fix` to switch back to main.
2. Doctor check `pre-checkout-hook`: Verifies git pre-checkout hook is
installed. The hook blocks checkout from main to any other branch.
Fixable via `gt doctor --fix` or `gt git-init`.
3. Runtime warning in all gt commands: Non-blocking warning if town root
is on wrong branch, with fix instructions.
The root cause of this issue was git commands running in the wrong
directory, switching the town root to a polecat branch. This broke gt
commands because rigs.json and other configs were on main, not the
polecat branch.
Closes: hq-1kwuj
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
ba76bf1232