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>

frontend/src/contexts/SessionContext.jsx

@@ -389,6 +389,33 @@ export function SessionProvider({ children }) {
         break;
       }
 
+      case 'system': {
+        // System events from Claude - log full event for debugging
+        console.log(`[${sessionId}] System event:`, event.subtype, JSON.stringify(event, null, 2));
+
+        // Check for context info in system init event
+        if (event.subtype === 'init') {
+          // Log all fields to find context info
+          console.log(`[${sessionId}] System init fields:`, Object.keys(event));
+        }
+
+        // Parse context message if present
+        if (event.message) {
+          const contextMatch = event.message.match(/Context left[^:]*:\s*(\d+)%/i);
+          if (contextMatch) {
+            const contextLeft = parseInt(contextMatch[1], 10);
+            console.log(`[${sessionId}] Context left:`, contextLeft + '%');
+            updateSession(sessionId, (session) => ({
+              stats: {
+                ...(session.stats || {}),
+                contextLeftPercent: contextLeft,
+              },
+            }));
+          }
+        }
+        break;
+      }
+
       default:
         console.log(`[${sessionId}] Unhandled claude event:`, type, event);
     }
@@ -795,6 +822,16 @@ export function SessionProvider({ children }) {
     updateSession(sessionId, { unreadCount: 0 });
   }, [updateSession]);
 
+  // Set compacting state
+  const setCompacting = useCallback((sessionId, value) => {
+    updateSession(sessionId, {
+      stats: {
+        ...(sessions[sessionId]?.stats || {}),
+        isCompacting: value,
+      },
+    });
+  }, [updateSession, sessions]);
+
   // Change permission mode
   const changePermissionMode = useCallback((sessionId, mode) => {
     const ws = wsRefs.current[sessionId];
@@ -900,6 +937,7 @@ export function SessionProvider({ children }) {
     sendMessage,
     stopGeneration,
     clearMessages,
+    setCompacting,
 
     // Permissions
     changePermissionMode,
@@ -909,7 +947,7 @@ export function SessionProvider({ children }) {
     createSession, closeSession, removeSession, renameSession, updateSessionConfig,
     setFocusedSessionId, markAsRead, reorderTabs, addToSplit, removeFromSplit, clearSplit,
     connectSession, disconnectSession, startClaudeSession, stopClaudeSession,
-    sendMessage, stopGeneration, clearMessages, changePermissionMode, respondToPermission,
+    sendMessage, stopGeneration, clearMessages, setCompacting, changePermissionMode, respondToPermission,
   ]);
 
   return (