UI/UX D3: dark mode toggle, chat export, accessibility, onboarding modal

- app.py: _JS with dark mode toggle (localStorage + system preference) (D3-17)
- app.py: dark mode CSS overrides for custom chat bubble colors (D3-17)
- app.py: export_chat() -> gr.File .md download button in controls row (D3-18)
- app.py: JS aria-label/role/aria-live injection for chatbot and inputs (D3-19)
- app.py: :focus-visible CSS 3px blue outline for keyboard navigation (D3-19)
- app.py: first-visit onboarding modal with localStorage guard (D3-20)
- app.py: js=_JS wired into gr.Blocks()
- ROADMAP.md: mark all D3 items complete

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

app.py

@@ -164,6 +164,24 @@ async def reset_chat(user_id):
     return [], []
 
 
+async def export_chat(history):
+    if not history:
+        return gr.update(visible=False)
+    from datetime import datetime
+    import tempfile
+    lines = [f"# 율봇 대화 내보내기\n_내보낸 시각: {datetime.now().strftime('%Y-%m-%d %H:%M')}_\n\n"]
+    for msg in history:
+        role = "👤 사용자" if msg["role"] == "user" else "🤖 율봇"
+        content = str(msg.get("content") or "")
+        lines.append(f"### {role}\n\n{content}\n\n---\n\n")
+    tmp = tempfile.NamedTemporaryFile(
+        mode="w", suffix=".md", delete=False, encoding="utf-8", prefix="youlbot_chat_"
+    )
+    tmp.write("".join(lines))
+    tmp.close()
+    return gr.update(value=tmp.name, visible=True)
+
+
 # ── 문서 관리 ─────────────────────────────────────────────────────
 
 async def ingest_files(files):
@@ -272,6 +290,69 @@ def _sources_html(sources: list) -> str:
     )
 
 
+_JS = """
+() => {
+    const htmlEl = document.documentElement;
+
+    // D3-17: 다크 모드 토글
+    window.toggleDarkMode = function() {
+        htmlEl.classList.toggle('dark');
+        const isDark = htmlEl.classList.contains('dark');
+        localStorage.setItem('youlbot_theme', isDark ? 'dark' : 'light');
+        const btn = document.getElementById('dark-mode-btn');
+        if (btn) btn.textContent = isDark ? '☀️' : '🌙';
+    };
+    const saved = localStorage.getItem('youlbot_theme');
+    if (saved === 'dark' || (!saved && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
+        htmlEl.classList.add('dark');
+    }
+
+    // D3-19: aria 레이블 설정
+    function addAriaLabels() {
+        const ta = document.querySelector('textarea[placeholder*="질문"]');
+        if (ta) ta.setAttribute('aria-label', '질문 입력창 (Enter 키로 전송)');
+        document.querySelectorAll('.send-btn').forEach(b => b.setAttribute('aria-label', '메시지 전송'));
+        const cb = document.getElementById('main-chatbot');
+        if (cb) { cb.setAttribute('role', 'log'); cb.setAttribute('aria-live', 'polite'); cb.setAttribute('aria-label', '대화 내용'); }
+    }
+
+    // D3-20: 첫 방문 온보딩 모달
+    function showOnboarding() {
+        if (localStorage.getItem('youlbot_onboarded')) return;
+        const modal = document.createElement('div');
+        modal.id = 'youlbot-onboarding';
+        modal.innerHTML = `
+<div style="position:fixed;inset:0;background:rgba(15,23,42,.55);backdrop-filter:blur(4px);z-index:9999;display:flex;align-items:center;justify-content:center;padding:16px;">
+  <div style="background:#fff;border-radius:20px;padding:36px 32px;max-width:400px;width:100%;box-shadow:0 24px 64px rgba(0,0,0,.25);">
+    <div style="font-size:2.4rem;text-align:center;margin-bottom:12px;">🤖</div>
+    <h2 style="margin:0 0 6px;font-size:1.3rem;font-weight:700;text-align:center;color:#1e293b;">율봇에 오신 것을 환영합니다!</h2>
+    <p style="margin:0 0 20px;text-align:center;color:#64748b;font-size:.875rem;">육아·금융 전문 AI 상담 도우미</p>
+    <ul style="list-style:none;padding:0;margin:0 0 24px;display:flex;flex-direction:column;gap:10px;">
+      <li style="display:flex;align-items:center;gap:10px;font-size:.9rem;color:#374151;"><span>💬</span> 아래 입력창에 질문을 입력하세요</li>
+      <li style="display:flex;align-items:center;gap:10px;font-size:.9rem;color:#374151;"><span>💡</span> 예시 질문 클릭으로 빠르게 시작</li>
+      <li style="display:flex;align-items:center;gap:10px;font-size:.9rem;color:#374151;"><span>📄</span> 문서 등록 탭에서 RAG 문서 추가</li>
+      <li style="display:flex;align-items:center;gap:10px;font-size:.9rem;color:#374151;"><span>🎤</span> 음성으로도 질문 가능</li>
+    </ul>
+    <button onclick="window.closeOnboarding()" style="width:100%;padding:13px;background:#3b82f6;color:#fff;border:none;border-radius:10px;font-size:.95rem;font-weight:600;cursor:pointer;" onmouseover="this.style.background='#2563eb'" onmouseout="this.style.background='#3b82f6'">시작하기</button>
+  </div>
+</div>`;
+        document.body.appendChild(modal);
+    }
+    window.closeOnboarding = function() {
+        const m = document.getElementById('youlbot-onboarding');
+        if (m) m.remove();
+        localStorage.setItem('youlbot_onboarded', '1');
+    };
+
+    setTimeout(function() {
+        addAriaLabels();
+        showOnboarding();
+        const btn = document.getElementById('dark-mode-btn');
+        if (btn && htmlEl.classList.contains('dark')) btn.textContent = '☀️';
+    }, 1500);
+}
+"""
+
 _CUSTOM_CSS = """
 footer { display: none !important; }
 
@@ -314,6 +395,18 @@ footer { display: none !important; }
     .app-header { flex-wrap: wrap; gap: 8px; }
     .message-wrap .user, .message-wrap .bot { max-width: 92% !important; }
 }
+
+/* 접근성: 포커스 표시 강화 (D3-19) */
+:focus-visible {
+    outline: 3px solid #3b82f6 !important;
+    outline-offset: 2px !important;
+    border-radius: 4px;
+}
+
+/* 다크 모드 커스텀 요소 오버라이드 (D3-17) */
+.dark .message-wrap .user { background: #1e3a5f !important; border-color: #2563eb !important; }
+.dark .message-wrap .bot  { background: #1e293b !important; border-color: #334155 !important; }
+.dark .app-header { border-color: #334155 !important; }
 """
 
 _THEME = gr.themes.Soft(
@@ -322,7 +415,7 @@ _THEME = gr.themes.Soft(
     neutral_hue="slate",
 )
 
-with gr.Blocks(title="율봇", css=_CUSTOM_CSS, theme=_THEME) as demo:
+with gr.Blocks(title="율봇", css=_CUSTOM_CSS, theme=_THEME, js=_JS) as demo:
     with gr.Row(elem_classes=["app-header"]):
         gr.HTML("""
 <div style="display:flex;align-items:center;gap:14px;padding:4px 0;">
@@ -333,6 +426,15 @@ with gr.Blocks(title="율봇", css=_CUSTOM_CSS, theme=_THEME) as demo:
     </div>
 </div>
 """)
+        gr.HTML("""
+<div style="display:flex;justify-content:flex-end;align-items:center;height:100%;">
+  <button id="dark-mode-btn" onclick="toggleDarkMode()" title="다크/라이트 모드 전환"
+    style="background:none;border:1.5px solid #e2e8f0;border-radius:8px;cursor:pointer;
+           font-size:1.2rem;padding:6px 10px;line-height:1;color:#64748b;transition:all .15s;"
+    onmouseover="this.style.borderColor='#94a3b8'"
+    onmouseout="this.style.borderColor='#e2e8f0'">🌙</button>
+</div>
+""", scale=0, min_width=60)
         user_selector = gr.Dropdown(
             choices=USER_LABELS,
             value=DEFAULT_USER,
@@ -390,8 +492,12 @@ with gr.Blocks(title="율봇", css=_CUSTOM_CSS, theme=_THEME) as demo:
                 with gr.Row():
                     show_thinking = gr.Checkbox(label="사고 과정 표시", value=True)
                     use_tts = gr.Checkbox(label="음성으로 답변 읽기 (TTS)", value=False)
-            with gr.Column(scale=1, min_width=120):
-                reset_btn = gr.Button("대화 초기화", size="sm")
+            with gr.Column(scale=2, min_width=240):
+                with gr.Row():
+                    export_btn = gr.Button("💾 내보내기", size="sm", min_width=100)
+                    reset_btn = gr.Button("대화 초기화", size="sm", min_width=100)
+
+        export_file = gr.File(label="내보내기 파일", visible=False)
 
         tts_output = gr.Audio(label="음성 답변", autoplay=True, visible=False)
         use_tts.change(lambda v: gr.Audio(visible=v), inputs=[use_tts], outputs=[tts_output])
@@ -412,6 +518,7 @@ with gr.Blocks(title="율봇", css=_CUSTOM_CSS, theme=_THEME) as demo:
         send_btn.click(respond, inputs=_respond_inputs, outputs=_respond_outputs)
         msg_box.submit(respond, inputs=_respond_inputs, outputs=_respond_outputs)
         reset_btn.click(reset_chat, inputs=[user_state], outputs=[chatbot, run_ids_state])
+        export_btn.click(export_chat, inputs=[chatbot], outputs=[export_file])
 
         chatbot.like(
             handle_feedback,