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/controllers/bo/popover_controller.ts

@@ -0,0 +1,19 @@
+import { Controller } from '@hotwired/stimulus';
+import { Popover } from 'bootstrap';
+
+export default class extends Controller {
+    popovers: Popover[] = [];
+
+    connect(): void {
+        this.popovers = [
+            ...this.element.querySelectorAll('[data-bs-toggle="popover"]'),
+        ]
+            .map((popoverTriggerEl) =>
+                Popover.getOrCreateInstance(popoverTriggerEl)
+            );
+    }
+
+    disconnect(): void {
+        this.popovers.forEach((popover) => popover.dispose());
+    }
+}