feat: auto-create Gemini CLI extension folder and files

[RajaPremSai]

This PR fixes #17 by adding automatic creation of the Gemini CLI extension folder
.gemini/extensions/spec-kit/ along with gemini-extension.json and GEMINI.md.

• Adds helper function setup_gemini_extension
• Ensures files are created on specify init --ai gemini
• Adds tests for extension setup
• Updates README to document this behavior

[Gaimchng3rjacob]

Awesome

[Gaimchng3rjacob]

fixes #17: Automates Gemini CLI extension scaffolding

• Adds setup_gemini_extension helper to initialize .gemini/extensions/spec-kit/
• Generates gemini-extension.json and GEMINI.md on specify init --ai gemini
• Includes tests for extension setup and file integrity
• Updates README to document Gemini extension behavior and onboarding flow

git commit -m "fixes #17: Automates Gemini CLI extension scaffolding

• Adds setup_gemini_extension helper to initialize .gemini/extensions/spec-kit/
• Generates gemini-extension.json and GEMINI.md on specify init --ai gemini
• Includes tests for extension setup and file integrity
• Updates README to document Gemini extension behavior and onboarding flow

This commit ritualizes Gemini module creation, ensuring every AI extension begins with clarity, structure, and symbolic authorship."

[Gaimchng3rjacob]

Appreciate the update—this works well with the extension logic. Good to go from my side ✅