feat: Add health check endpoint

Introduce a new health check endpoint at `/api/health`. This endpoint
returns a JSON response indicating the server's status and configuration
details, such as the port, data path, and configured URLs for external
services.

This change also refactors the application setup by:
- Creating a `lib.rs` file to house the `create_router` function, making
  it
  reusable for both the main application and integration tests.
- Moving configuration loading logic into `main.rs` and passing it as a
  shared state (`Arc<Config>`) to the router.
- Adding a unit test (`health_test.rs`) to verify the functionality of
  the
  health check endpoint.
- Updating `Cargo.toml` and `Cargo.lock` to include the `tower`
  dependency,
  which is used for testing.

server/src/lib.rs

@@ -0,0 +1,14 @@
+pub mod config;
+pub mod error;
+pub mod routes;
+
+use std::sync::Arc;
+
+use axum::Router;
+
+use config::Config;
+
+/// Build the application router. Used by main.rs and integration tests.
+pub fn create_router(config: Arc<Config>) -> Router {
+    routes::api_router().with_state(config)
+}

server/src/main.rs

@@ -1,12 +1,18 @@
-mod config;
-mod error;
-
-use config::Config;
 use std::sync::Arc;
 
+use tokio::net::TcpListener;
+
+use doctate_server::config::Config;
+
 #[tokio::main]
 async fn main() {
     dotenvy::dotenv().ok();
     let config = Arc::new(Config::from_env());
-    println!("Server starting on port {}", config.server_port);
+
+    let addr = format!("0.0.0.0:{}", config.server_port);
+    println!("Server starting on {addr}");
+
+    let app = doctate_server::create_router(config);
+    let listener = TcpListener::bind(&addr).await.unwrap();
+    axum::serve(listener, app).await.unwrap();
 }

server/src/routes/health.rs

@@ -0,0 +1,18 @@
+use std::sync::Arc;
+
+use axum::extract::State;
+use axum::Json;
+use serde_json::{json, Value};
+
+use crate::config::Config;
+
+pub async fn handle_health(State(config): State<Arc<Config>>) -> Json<Value> {
+    Json(json!({
+        "status": "ok",
+        "port": config.server_port,
+        "data_path": config.data_path.to_string_lossy(),
+        "users": config.users.iter().map(|u| &u.slug).collect::<Vec<_>>(),
+        "whisper_url": config.whisper_url,
+        "ollama_url": config.ollama_url,
+    }))
+}

server/src/routes/mod.rs

@@ -0,0 +1,11 @@
+mod health;
+
+use std::sync::Arc;
+
+use axum::Router;
+
+use crate::config::Config;
+
+pub fn api_router() -> Router<Arc<Config>> {
+    Router::new().route("/api/health", axum::routing::get(health::handle_health))
+}