Optimize git operations to only clone main branch

[robdimarco-atxp]

Summary

• Optimize git clone operations to reduce data transfer by only downloading the main branch with shallow history
• Apply optimizations to both demo cloning and project template cloning operations
• Maintain performance improvements for git pull operations on existing repositories

Changes

• Shallow clone: Added --depth 1 to download only the latest commit instead of full history
• Single branch: Added --single-branch to avoid downloading other branches
• Explicit branch: Added --branch main to explicitly target the main branch
• Optimized updates: Modified git pull to use --depth 1 and explicitly pull from origin main
• Documentation: Added comprehensive tests to document the expected git parameters

Performance Impact

• Reduced bandwidth: Significantly less data downloaded during git operations
• Faster clone times: Only downloading latest commit instead of full repository history
• Smaller disk usage: Repositories take up less space without full git history

Test plan

• Build and typecheck passes
• All existing tests pass
• New git optimization tests pass
• Manual testing confirms demo command works with optimized clone
• Verified shallow clone creates repository with only 1 commit in history
• Lint checks pass

Fixes: https://linear.app/novellum/issue/ATXP-250/the-cli-should-only-get-main-branch-when-cloning-the-demo

🤖 Generated with Claude Code

[linear]

ATXP-250 The CLI should only get main branch when cloning the demo

When cloning the demo, we do not need a git history and only need the main branch. Our current git clone gets the whole history. This is wasteful.