Add prompts directory to .gitignore

- Include `.github/prompts/*` to ignore prompt files

Author: chrimaho

.gitignore

@@ -7,6 +7,7 @@ Pipfile.lock
 .github/copilot-instructions.md
 git_output/
 .github/instructions/*
+.github/prompts/*
 .complexipy_cache/*
 
 # Byte-compiled / optimized / DLL files