feat(templates): add service language template management

Add normalized service and template catalogs, scoped administration, migration, validation, and regression coverage.

Ref: IT-1601

HrynCo.NotificationService.Web/wwwroot/js/service-editor.js

@@ -0,0 +1,36 @@
+(() => {
+    const form = document.getElementById('serviceForm');
+    const rows = document.getElementById('serviceLanguages');
+    const alert = document.getElementById('serviceLanguageAlert');
+    let sequence = rows.children.length;
+    let dirty = false;
+    function reindex() {
+        Array.from(rows.children).forEach((row, index) => row.querySelectorAll('[name]').forEach(input => {
+            input.name = input.name.replace(/Languages\[\d+\]/, `Languages[${index}]`);
+        }));
+    }
+    document.getElementById('addServiceLanguage').addEventListener('click', () => {
+        const fragment = document.createElement('template');
+        fragment.innerHTML = document.getElementById('serviceLanguageRow').innerHTML.replaceAll('__index__', String(sequence++));
+        rows.append(fragment.content);
+        reindex();
+        rows.lastElementChild.querySelector('input:not([type="hidden"])').focus();
+        dirty = true;
+    });
+    rows.addEventListener('click', event => {
+        const button = event.target.closest('.remove-service-language');
+        if (!button) return;
+        if (Number(button.dataset.count) > 0) {
+            alert.textContent = `Cannot remove this language: ${button.dataset.count} version(s) use it. Save other changes, then use the separate delete language and versions confirmation.`;
+            return;
+        }
+        button.closest('tr').remove();
+        reindex();
+        dirty = true;
+    });
+    form.addEventListener('input', () => { dirty = true; });
+    form.addEventListener('submit', () => { dirty = false; });
+    window.addEventListener('beforeunload', event => {
+        if (dirty) { event.preventDefault(); event.returnValue = ''; }
+    });
+})();