chore(repo): require signed-off commits

[abhiyandhakal]

What this changes

The Husky commit-msg hook now requires every commit message to include a valid Signed-off-by: Name <email> trailer. The existing Commitlint check still runs after the sign-off check.

Use git commit -s to have Git add the trailer automatically.

How to check it

• A signed-off commit was created successfully on this branch, and the commit hooks completed.
• To confirm the rejection path, try a commit without -s in a disposable checkout; the hook should reject it with a git commit -s hint.
• No test suite was run for this hook-only change.

Checklist

• Conventional commit title
• Commit is signed off
• No new dependency