Add runnable smoke-test clients for each SDK

Each package gets a small example program that exercises the real
client: with no ORIGIN_SERVICE_KEY set it runs against a local mock
check-in server, otherwise it checks in against ORIGIN_URL/Origin's
public endpoint. Wired into CI (mock mode) as a regression check, and
documented per README.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

rust/examples/testclient.rs

@@ -0,0 +1,91 @@
+//! Runnable smoke test for the Rust origin-client SDK.
+//!
+//! Without ORIGIN_SERVICE_KEY set, it spins up a local mock check-in server
+//! and exercises the client against it — no network, no credentials needed.
+//! With ORIGIN_SERVICE_KEY set, it performs a real check-in against
+//! ORIGIN_URL (or Origin's public endpoint) so the SDK can be smoke-tested
+//! end-to-end against a live server.
+//!
+//! Usage: `cargo run --example testclient [-- --watch]`
+
+use std::env;
+use std::sync::Arc;
+
+use origin_client::{Client, Config, FnLogger};
+use tokio_util::sync::CancellationToken;
+
+fn env_or(key: &str, default: &str) -> String {
+    env::var(key).unwrap_or_else(|_| default.to_string())
+}
+
+#[tokio::main]
+async fn main() {
+    let watch = env::args().any(|a| a == "--watch");
+
+    let mut cfg = Config {
+        url: env::var("ORIGIN_URL").ok(),
+        service_key: env::var("ORIGIN_SERVICE_KEY").unwrap_or_default(),
+        type_: env_or("ORIGIN_TYPE", "icy2-testclient"),
+        version: env_or("ORIGIN_VERSION", "0.0.0-test"),
+        name: env_or("ORIGIN_NAME", "icy2-testclient-local"),
+        site: env::var("ORIGIN_SITE").ok(),
+        environment: env::var("ORIGIN_ENVIRONMENT").ok(),
+        logger: Arc::new(FnLogger(|msg: &str, err| {
+            eprintln!("[warn] {msg}: {err:?}");
+        })),
+        ..Default::default()
+    };
+
+    // Held so the mock server stays alive for the client's lifetime; unused
+    // in real-endpoint mode.
+    let mut _mock_server = None;
+
+    if cfg.service_key.is_empty() {
+        println!("ORIGIN_SERVICE_KEY not set — using a local mock check-in server");
+        let mut server = mockito::Server::new_async().await;
+        server
+            .mock("POST", "/")
+            .with_status(200)
+            .with_header("content-type", "application/json")
+            .with_body(
+                r#"{"success":true,"service_instance_id":1,"unique_install_id":"test-install-id","status":"provisioning","pinged_at":"2026-08-01T00:00:00Z"}"#,
+            )
+            .create_async()
+            .await;
+
+        cfg.url = Some(server.url());
+        cfg.service_key = "test-key".to_string();
+        cfg.install_id = Some("test-install-id".to_string());
+        _mock_server = Some(server);
+    }
+
+    if let Ok(h) = env::var("ORIGIN_INTERVAL_HOURS") {
+        if let Ok(n) = h.parse() {
+            cfg.interval_hours = Some(n);
+        }
+    }
+
+    let client = Client::new(cfg).expect("origin_client::Config validation failed");
+
+    if watch {
+        println!("watching — Ctrl-C to stop");
+        let cancel = CancellationToken::new();
+        let cancel_clone = cancel.clone();
+        tokio::spawn(async move {
+            tokio::signal::ctrl_c().await.ok();
+            cancel_clone.cancel();
+        });
+        client.run(cancel).await;
+        return;
+    }
+
+    match client.checkin_once().await {
+        Ok(resp) => {
+            println!("{resp:#?}");
+        }
+        Err(err) => {
+            eprintln!("checkin failed: {err}");
+            std::process::exit(1);
+        }
+    }
+}