Function init_lua_extensions 

pub fn init_lua_extensions(
    user_config_dir: &Path,
    project_dir: Option<&Path>,
    tools: &mut ToolRegistry,
    policy: &LuaCapabilityPolicy,
) -> Option<Arc<Mutex<LuaRuntime>>>

Discover and load Lua extensions from user and project directories, registering any tools they define onto the given registry.

Returns the shared runtime handle (for command dispatch and hot-reload). Returns None if no extensions were found or the runtime failed to start.