Add dirty check to all remaining editor modals

Subclass Modal with snapshotValues() for: value source editor, audio
source editor, add device, profile editor, capture template, stream
editor, and PP template modals. Close/cancel now triggers discard
confirmation when form has unsaved changes. Document the convention
in CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/js/features/audio-sources.js

@@ -17,7 +17,22 @@ import { showToast, showConfirm } from '../core/ui.js';
 import { Modal } from '../core/modal.js';
 import { loadPictureSources } from './streams.js';
 
-const audioSourceModal = new Modal('audio-source-modal');
+class AudioSourceModal extends Modal {
+    constructor() { super('audio-source-modal'); }
+
+    snapshotValues() {
+        return {
+            name: document.getElementById('audio-source-name').value,
+            description: document.getElementById('audio-source-description').value,
+            type: document.getElementById('audio-source-type').value,
+            device: document.getElementById('audio-source-device').value,
+            parent: document.getElementById('audio-source-parent').value,
+            channel: document.getElementById('audio-source-channel').value,
+        };
+    }
+}
+
+const audioSourceModal = new AudioSourceModal();
 
 // ── Modal ─────────────────────────────────────────────────────
 
@@ -60,10 +75,11 @@ export async function showAudioSourceModal(sourceType, editData) {
     }
 
     audioSourceModal.open();
+    audioSourceModal.snapshot();
 }
 
-export function closeAudioSourceModal() {
-    audioSourceModal.forceClose();
+export async function closeAudioSourceModal() {
+    await audioSourceModal.close();
 }
 
 export function onAudioSourceTypeChange() {