fix(shell): stale tabs now know the gateway was updated

Recurring confusion all day: the SPA lives in an open tab until reload, so
after a gateway rebuild/update users kept seeing (and benchmarking with!) an
old interface — "where is the feature", "why are the test ids old". The meta
endpoint now carries the process start timestamp; the existing 20s health
poll compares it, and when the gateway has restarted the tab shows a fixed
banner: "The gateway was updated — this page is running an older interface"
with a one-click Reload. 2 strings in all 7 languages.

src/admin/mod.rs

@@ -600,8 +600,18 @@ async fn provider_models(
 }
 
 async fn meta(State(state): State<SharedState>) -> ApiResult {
+    // process start marker: open tabs poll this and offer a reload when the
+    // gateway (and thus the embedded SPA) has been restarted/updated
+    static STARTED: std::sync::OnceLock<u64> = std::sync::OnceLock::new();
+    let started = *STARTED.get_or_init(|| {
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs()
+    });
     ok(json!({
         "version": env!("CARGO_PKG_VERSION"),
+        "started": started,
         "update_available": state.gateway_update.lock().unwrap().clone(),
         "admin_open_public": state
             .admin_open_public