feat: protect unsaved camera work

apps/acoustic-camera/index.html

@@ -61,7 +61,7 @@
           </section>
 
           <section class="history-section">
-            <div class="section-heading"><div><p class="eyebrow">Same-scene comparison</p><h2>배열 비교 기록</h2></div><button class="text-button" id="clear-history-button" type="button">기록 비우기</button></div>
+            <div class="section-heading"><div><p class="eyebrow">Same-scene comparison</p><h2>배열 비교 기록</h2></div><div class="history-actions"><button class="text-button" id="export-history-button" type="button" disabled>전체 기록 JSON</button><button class="text-button" id="clear-history-button" type="button">기록 비우기</button></div></div>
             <p class="section-copy">비교 배열 또는 Array JSON을 바꿔 다시 실행하면 같은 scene·scan·STFT 결과를 이 세션에서 나란히 비교합니다.</p>
             <div class="history-list" id="history-list"></div>
           </section>
@@ -124,7 +124,13 @@
             <div class="band-editor-list" id="band-list"></div>
           </section>
 
-          <section class="output-card"><button class="button button--ghost button--full" id="export-experiment-button" type="button">Experiment JSON 저장</button></section>
+          <section class="output-card">
+            <div class="output-actions">
+              <button class="button button--ghost" id="export-scene-button" type="button">Scene JSON 저장</button>
+              <button class="button button--ghost" id="export-experiment-button" type="button">Experiment JSON 저장</button>
+            </div>
+            <p class="output-save-state" id="output-save-state">저장하지 않은 변경 없음</p>
+          </section>
 
           <section class="validation-card" aria-live="polite">
             <div class="validation-dot" id="validation-dot"></div>