refactor(app): clarify application and binary roles

Rename the application Cargo package from irtt-cli to irtt-rs
(crates/irtt-cli -> crates/irtt-app), and hard-rename its scriptable
client binary from irtt-cli to irtt-client, now that the application
also ships a first-class server and the old name reads as an umbrella
CLI for both roles.

Give each dedicated binary (irtt-client, irtt-tui, irtt-server) its
own entry point instead of funneling through the multicall
dispatcher's argv0/subcommand logic, so a dedicated binary only links
the applet code for the role it implements and always runs that role
regardless of the name it's invoked or copied under. irtt-rs remains
the feature-selectable multicall dispatcher and is now the only binary
that inspects argv0 or subcommands.

Move future application releases to the irtt-rs/vX.Y.Z tag namespace
(regenerated via `dist generate`), and bump the application package to
0.6.0 as a breaking distribution change. Library crate versions are
unaffected.

crates/irtt-app/src/entry.rs

@@ -0,0 +1,136 @@
+use std::{
+    env,
+    ffi::OsString,
+    process::ExitCode,
+    sync::{atomic::AtomicBool, Arc},
+};
+
+use crate::{
+    applet::{dispatch_from_argv, AppletDispatch, RequestedApplet},
+    signal::install_signal_handler,
+};
+
+/// Entry point for the `irtt-rs` multicall dispatcher binary.
+///
+/// Chooses an applet by subcommand or by recognized argv0 and may reference
+/// every applet enabled by the active feature set.
+pub fn dispatcher_main() -> ExitCode {
+    run_with_exit_code("irtt-rs", run_dispatcher_from_env)
+}
+
+/// Entry point for the dedicated `irtt-client` binary.
+///
+/// Runs the stream client directly; it never consults argv0 or the applet
+/// dispatcher, so a renamed or copied executable still runs the client.
+#[cfg(feature = "client")]
+pub fn client_main() -> ExitCode {
+    run_with_exit_code("irtt-client", || {
+        run_client_applet(env::args_os().collect())
+    })
+}
+
+/// Entry point for the dedicated `irtt-tui` binary.
+///
+/// Runs the terminal UI directly; it never consults argv0 or the applet
+/// dispatcher, so a renamed or copied executable still runs the TUI.
+#[cfg(feature = "tui")]
+pub fn tui_main() -> ExitCode {
+    run_with_exit_code("irtt-tui", || run_tui_applet(env::args_os().collect()))
+}
+
+/// Entry point for the dedicated `irtt-server` binary.
+///
+/// Runs the server directly; it never consults argv0 or the applet
+/// dispatcher, so a renamed or copied executable still runs the server.
+#[cfg(feature = "server")]
+pub fn server_main() -> ExitCode {
+    run_with_exit_code("irtt-server", || {
+        run_server_applet(env::args_os().collect())
+    })
+}
+
+fn run_with_exit_code(
+    program: &str,
+    f: impl FnOnce() -> Result<(), Box<dyn std::error::Error>>,
+) -> ExitCode {
+    match f() {
+        Ok(()) => ExitCode::SUCCESS,
+        Err(err) => {
+            eprintln!("{program}: {err}");
+            ExitCode::FAILURE
+        }
+    }
+}
+
+fn run_dispatcher_from_env() -> Result<(), Box<dyn std::error::Error>> {
+    let argv: Vec<OsString> = env::args_os().collect();
+    let (requested, argv) = match dispatch_from_argv(argv)? {
+        AppletDispatch::Run { applet, argv } => (applet, argv),
+        AppletDispatch::Help(help) => {
+            print!("{help}");
+            return Ok(());
+        }
+    };
+
+    match requested {
+        RequestedApplet::Client => run_client_applet(argv),
+        RequestedApplet::Tui => run_tui_applet(argv),
+        RequestedApplet::Server => run_server_applet(argv),
+    }
+}
+
+/// Installs the shutdown signal handler shared by every applet and hands the
+/// resulting flag to `f`.
+fn with_shutdown_flag(
+    f: impl FnOnce(&AtomicBool) -> Result<(), Box<dyn std::error::Error>>,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let shutdown_requested = Arc::new(AtomicBool::new(false));
+    install_signal_handler(Arc::clone(&shutdown_requested))
+        .map_err(|err| format!("failed to install signal handler: {err}"))?;
+    f(shutdown_requested.as_ref())
+}
+
+#[cfg(feature = "client")]
+fn run_client_applet(argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    use clap::Parser;
+
+    with_shutdown_flag(|shutdown_requested| {
+        let args = crate::cmd::client::ClientArgs::parse_from(argv);
+        crate::cmd::client::run_stream(args, shutdown_requested)
+    })
+}
+
+#[cfg(not(feature = "client"))]
+fn run_client_applet(_argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    Err("client applet is not available; rebuild with the client feature".into())
+}
+
+#[cfg(feature = "server")]
+fn run_server_applet(argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    use clap::Parser;
+
+    with_shutdown_flag(|shutdown_requested| {
+        let args = crate::cmd::server::ServerArgs::parse_from(argv);
+        crate::cmd::server::run_server(args, shutdown_requested)
+    })
+}
+
+#[cfg(not(feature = "server"))]
+fn run_server_applet(_argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    Err("server applet is not available; rebuild with the server feature".into())
+}
+
+#[cfg(feature = "tui")]
+fn run_tui_applet(argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    use clap::Parser;
+
+    with_shutdown_flag(|shutdown_requested| {
+        let args = crate::cmd::tui::TuiArgs::parse_from(argv);
+        crate::cmd::tui::run_tui(args, shutdown_requested)
+    })
+}
+
+#[cfg(not(feature = "tui"))]
+fn run_tui_applet(_argv: Vec<OsString>) -> Result<(), Box<dyn std::error::Error>> {
+    Err("TUI applet is not available; rebuild with the tui feature".into())
+}