Add cookieless analytics, kept out of the repository

.gitignore

@@ -16,10 +16,8 @@ coverage/
 
 # Environment files
 .env
-.env.local
-.env.development.local
-.env.test.local
-.env.production.local
+.env.*
+!.env.example
 
 # Python
 __pycache__/

frontend/.env.example

@@ -0,0 +1,10 @@
+# Umami website ID, from the tracking code panel in the Umami dashboard.
+#
+# Copy this file to .env.production.local and paste the ID in. That file is
+# gitignored, and `vite build` reads it while `vite dev` does not — so the ID
+# never enters the repository, and running the dev server does not put localhost
+# traffic in the stats.
+#
+# Leave it empty, or skip the file entirely, and analytics are a no-op: no script
+# tag, no requests. That is what a fork gets.
+VITE_UMAMI_WEBSITE_ID=

frontend/src/main.tsx

@@ -4,6 +4,11 @@ import App from './App.tsx';
 import { Provider } from './context/provider.tsx';
 import './index.css';
 import './styles/scrollbars.css';
+import { initAnalytics } from './utils/analytics.ts';
+
+// Straight to the document rather than through a component, since it has nothing
+// to say about the tree.
+initAnalytics();
 
 createRoot(document.getElementById('root')!).render(
     <StrictMode>

frontend/src/utils/analytics.ts

@@ -0,0 +1,30 @@
+/**
+ * Umami, injected at runtime and only when a website ID was built in.
+ *
+ * The ID comes from `.env.production.local`, which is gitignored, so a clone or
+ * a fork gets no script tag, no request and no ID — analytics are simply absent
+ * rather than broken or pointed at someone else's account. See `.env.example`.
+ *
+ * `.env.production.local` is read by `vite build` and never by `vite dev`, so
+ * working locally cannot put localhost traffic in the stats. The `PROD` guard
+ * says the same thing twice, in case the value is ever put in a file the dev
+ * server does read.
+ *
+ * Umami is cookieless, which is why there is no consent banner in the app.
+ * Anything added here that sets a cookie changes that.
+ */
+const websiteId = import.meta.env.VITE_UMAMI_WEBSITE_ID;
+
+export function initAnalytics() {
+    if (!websiteId || !import.meta.env.PROD) return;
+
+    const script = document.createElement('script');
+    script.src = 'https://cloud.umami.is/script.js';
+    // The tracker reads its configuration off `document.currentScript`, so the
+    // attributes have to be set before it is appended, and it has to stay a
+    // classic script — as a module `currentScript` is null and it gives up
+    // without a word. For the same reason there is no `data-host-url`: absent,
+    // it defaults to Umami Cloud's own endpoint.
+    script.setAttribute('data-website-id', websiteId);
+    document.head.appendChild(script);
+}

frontend/src/vite-env.d.ts

@@ -0,0 +1,6 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+    /** Umami website ID. Optional: absent from any build but the live one. */
+    readonly VITE_UMAMI_WEBSITE_ID?: string;
+}