feat: Add slash commands and help dialog

- Restore slash command autocomplete (type "/" to see suggestions)
- Add /compact command to trigger context compaction
- Add /clear command to clear chat history
- Add /help command with styled modal dialog
- Add HelpDialog component with command list
- Add system event handler for context warnings
- Add debug logging for all Claude events to /tmp/claude-events-debug.jsonl

TODO: Parse context warning from Claude events when identified

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/server.js

@@ -837,6 +837,20 @@ wss.on('connection', async (ws, req) => {
             // Note: ExitPlanMode is now handled exclusively via Control Protocol (can_use_tool)
             // to avoid tool_result/control_response confusion and message compaction issues
 
+            // Debug: Write all events to file for context analysis
+            const debugLogPath = '/tmp/claude-events-debug.jsonl';
+            const debugEntry = {
+              timestamp: new Date().toISOString(),
+              sessionId,
+              event
+            };
+            try {
+              const fs = await import('fs');
+              fs.appendFileSync(debugLogPath, JSON.stringify(debugEntry) + '\n');
+            } catch (e) {
+              // Ignore write errors
+            }
+
             sendToClient('claude_event', { event });
           } catch (e) {
             // Non-JSON output, send as raw
@@ -848,10 +862,26 @@ wss.on('connection', async (ws, req) => {
     });
 
     // Handle stderr
-    claudeProcess.stderr.on('data', (data) => {
+    claudeProcess.stderr.on('data', async (data) => {
       const content = data.toString();
       // Always log stderr for SSH connections (exit code 255 debugging)
       if (DEBUG || isSSH) console.log(`[${sessionId}] stderr:`, content);
+
+      // Debug: Write stderr to file for context analysis
+      const debugLogPath = '/tmp/claude-events-debug.jsonl';
+      const debugEntry = {
+        timestamp: new Date().toISOString(),
+        sessionId,
+        type: 'stderr',
+        content
+      };
+      try {
+        const fs = await import('fs');
+        fs.appendFileSync(debugLogPath, JSON.stringify(debugEntry) + '\n');
+      } catch (e) {
+        // Ignore write errors
+      }
+
       sendToClient('stderr', { content });
     });