feat: add --generate-config mode to output default config

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/args.rs

@@ -63,6 +63,10 @@ pub struct ModeArgs {
     #[arg(help("Start REST HTTP server"))]
     pub server: bool,
 
+    #[arg(group("mode"), help_heading("Mode Options"), long, conflicts_with_all(["save", "get", "diff", "list", "delete", "info", "status", "server"]))]
+    #[arg(help("Generate default configuration and output to stdout"))]
+    pub generate_config: bool,
+
     #[arg(help_heading("Server Options"), long, env("KEEP_SERVER_ADDRESS"))]
     #[arg(help("Server address to bind to"))]
     pub server_address: Option<String>,