Generate Cursor rules for Rill projects with template

[grahamplata]

Allows a user to generate Cursor rules for Rill projects with the CLI.

• Adding Cursor rules to an existing project
• Generating an empty project with Cursor rules

# Example adding cursor rules
rill init --template cursor
rill init <my existing project> --template cursor

Checklist:

• [x] Covered by tests
• [x] Ran it and it works as intended
• [ ] Reviewed the diff before requesting a review
• [ ] Checked for unhandled edge cases
• [x] Linked the issues it closes
• [x] Checked if the docs need to be updated. If so, create a separate Linear DOCS issue - (Yes will need to be generated)
• [x] Intend to cherry-pick into the release branch
• [ ] I'm proud of this work!