feat: add /health endpoint for Fly.io health checks

- Add lightweight GET /health returning {"status":"ok"}
- Update fly.toml to use /health instead of /

fly.toml

@@ -25,7 +25,7 @@ interval = '30s'
 timeout = '5s'
 grace_period = '10s'
 method = 'GET'
-path = '/'
+path = '/health'
 
 [mounts]
 source = 'brewlog_data'

src/application/routes/app/mod.rs

@@ -39,6 +39,7 @@ pub(super) fn router() -> axum::Router<AppState> {
         .route("/components/donut-chart.js", get(donut_chart_js))
         .route("/favicon-light.svg", get(favicon_light))
         .route("/favicon-dark.svg", get(favicon_dark))
+        .route("/health", get(health))
 }
 
 async fn scan_redirect() -> Redirect {
@@ -134,3 +135,10 @@ async fn favicon_dark() -> impl IntoResponse {
         include_str!("../../../../static/favicon-dark.svg"),
     )
 }
+
+async fn health() -> impl IntoResponse {
+    (
+        [("content-type", "application/json")],
+        r#"{"status":"ok"}"#,
+    )
+}