feat: add GNU screen wrapping with process monitor

Add screen session management infrastructure:
- ScreenManager class to create, track, and kill GNU screen sessions
- Persistence of screen sessions to ~/.claudeman/screens.json
- Process stats collection (memory, CPU, child count)
- Reconciliation to detect dead/orphan screens

New API endpoints:
- GET /api/screens - list screens with stats
- DELETE /api/screens/:sessionId - kill screen
- POST /api/screens/reconcile - find dead screens
- POST /api/screens/stats/start|stop - control stats polling

New Process Monitor panel:
- Slide-up panel with real-time stats (2s updates)
- Shows memory, CPU, child processes per screen
- Kill button for each screen session
- Reconcile button to clean up dead screens

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/public/index.html

@@ -98,6 +98,7 @@
 
         <button class="btn-toolbar" onclick="app.copyTerminal()" title="Copy terminal">Copy</button>
         <button class="btn-toolbar" onclick="app.clearTerminal()" title="Clear terminal (Ctrl+L)">Clear</button>
+        <button class="btn-toolbar" onclick="app.toggleProcessPanel()" title="Process Monitor">Processes</button>
 
         <div class="toolbar-divider"></div>
 
@@ -226,6 +227,20 @@
       </div>
     </div>
 
+    <!-- Process Monitor Panel (slide-up) -->
+    <div class="process-panel" id="processPanel">
+      <div class="process-panel-header">
+        <span>Process Monitor</span>
+        <div class="process-panel-actions">
+          <button class="btn-toolbar btn-sm" onclick="app.reconcileScreens()" title="Check for dead screens">Reconcile</button>
+          <button class="btn-close" onclick="app.toggleProcessPanel()">&times;</button>
+        </div>
+      </div>
+      <div class="process-panel-body" id="processPanelBody">
+        <div class="process-empty">No screen sessions tracked</div>
+      </div>
+    </div>
+
     <!-- Task Tree Panel (slide-up) -->
     <div class="task-panel" id="taskPanel">
       <div class="task-panel-header">