feat: mobile response viewer — read full Claude responses via native scroll

Claude Code's Ink framework uses alternate screen buffer + VPA cursor
positioning, resulting in near-zero xterm.js scrollback on mobile.
Instead of fighting terminal scrollback, this adds a native scrollable
overlay that reads structured responses from Claude's JSONL transcripts.

- New API: GET /api/sessions/:id/last-response reads transcript JSONL
  - ?context=full returns full conversation thread (user + assistant)
  - Fallback to terminal buffer with ANSI stripping if no transcript
- Response viewer panel: bottom sheet with native iOS/Android scroll
- "More" button loads full conversation context as threaded view
- Eye icon in header bar (mobile only), no toolbar space impact

src/web/public/index.html

@@ -92,6 +92,7 @@
             <span class="stat-value" id="statMem">--</span>
           </div>
         </div>
+        <button class="btn-icon-header btn-response-viewer-header" onclick="app.toggleResponseViewer()" title="View last response" aria-label="View last response"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M1 12s4-8 11-8 11 8 11 8-4 8-11 8-11-8-11-8z"/><circle cx="12" cy="12" r="3"/></svg></button>
         <button class="btn-icon-header btn-notifications" onclick="app.toggleNotifications()" title="Notifications" aria-label="Toggle notifications">
           <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9"/><path d="M13.73 21a2 2 0 0 1-3.46 0"/></svg>
           <span class="notification-badge" id="notifBadge" style="display:none;">0</span>
@@ -331,6 +332,19 @@
       </div>
     </div>
 
+    <!-- Response Viewer (mobile: native-scroll overlay for reading full Claude responses) -->
+    <div class="response-viewer" id="responseViewer">
+      <div class="response-viewer-header">
+        <span id="responseViewerTitle">Last Response</span>
+        <div class="response-viewer-actions">
+          <button class="response-viewer-more" id="responseViewerMore" onclick="app.loadFullContext()">More</button>
+          <button class="response-viewer-close" onclick="app.toggleResponseViewer()">&times;</button>
+        </div>
+      </div>
+      <div class="response-viewer-body" id="responseViewerBody"></div>
+    </div>
+    <div class="response-viewer-backdrop" id="responseViewerBackdrop" onclick="app.toggleResponseViewer()"></div>
+
     <!-- Bottom Toolbar -->
     <footer class="toolbar">
       <div class="toolbar-left">