Improved Git Ignore for Checkpoints

What changed: Checkpoint gitignore now prevents duplicate entries and has better error logging

How it works now:

• Reads existing .gitignore before appending to avoid duplicates
• Uses structured error logging with explicit error levels
• Better path handling with trailing slashes
• Creates parent directories if needed

Details:

• More robust against repeated invocations
• Cleaner .gitignore files
• Better error reporting and telemetry
• Evidence: yy6() at line 412545, aY1() at line 404121 (enhanced from u35() and Z61() in v1.0.120)