Function load_predefined_commands 

pub fn load_predefined_commands() -> Vec<(String, String, String)>

Load all predefined commands from the embedded commands/ directory.

Returns a vec of (name, description, prompt_content) tuples.

• name: the slash command name without / prefix (e.g., "review")
• description: human-readable description for the dropdown
• prompt_content: the full prompt body sent as a user message

When multiple versions of a command exist (e.g., review.v1.md and review.v2.md), only the highest version is returned.