Migrate frontend to TypeScript with Deno-based tooling (#206)

Compiles assets/*.ts via sensiolabs/typescript-bundle (standalone SWC
binary) and adds Deno for formatting, linting, type-checking, and
tests, keeping the project's no-Node/npm approach intact. Wires all
four into CI, the Justfile, and the pre-commit hook.

assets/backoffice.ts

@@ -0,0 +1,43 @@
+import 'bootstrap/dist/css/bootstrap.min.css';
+import 'bootstrap-icons/font/bootstrap-icons.min.css';
+import './styles/backoffice.scss';
+import '@hotwired/turbo';
+import './stimulus.ts';
+import './bootstrap.ts';
+import * as Sentry from '@sentry/browser';
+
+const dsn = document.querySelector<HTMLMetaElement>('meta[name="sentry-dsn"]')
+    ?.content ?? '';
+const userEmail =
+    document.querySelector<HTMLMetaElement>('meta[name="user-email"]')
+        ?.content ?? '';
+
+// When no real DSN is configured, route to the local Spotlight sidecar so
+// nothing reaches Sentry. A syntactically valid DSN is still required for the
+// SDK to initialise; the tunnel option redirects all transport to Spotlight.
+const useSpotlight = !dsn;
+const effectiveDsn = dsn || 'https://0@o0.ingest.sentry.io/0';
+
+const feedbackIntegration = Sentry.feedbackIntegration({
+    colorScheme: 'system',
+    showName: false,
+    showEmail: true,
+    isEmailRequired: false,
+    autoInject: false,
+    triggerLabel: 'Report feedback',
+    formTitle: 'Report Feedback',
+    submitButtonLabel: 'Send Feedback',
+});
+
+Sentry.init({
+    dsn: effectiveDsn,
+    tunnel: useSpotlight ? 'http://localhost:8969/stream' : undefined,
+    integrations: [feedbackIntegration],
+});
+
+// autoInject is unreliable in Sentry v10 due to the setupOnce guard; mount manually.
+feedbackIntegration.createWidget();
+
+if (userEmail) {
+    Sentry.setUser({ email: userEmail });
+}