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/hooks/useClaudeSession.js

@@ -423,9 +423,12 @@ export function useClaudeSession() {
           isCompacting: false,
         }));
       }
-      // Detect compacting
-      if (event.message.includes('compact')) {
+      // Detect compacting start/end from Claude's system messages
+      const msg = event.message.toLowerCase();
+      if (msg.includes('compacting') || msg.includes('summarizing conversation')) {
         setSessionStats(prev => ({ ...prev, isCompacting: true }));
+      } else if (msg.includes('compacted') || msg.includes('summarized')) {
+        setSessionStats(prev => ({ ...prev, isCompacting: false }));
       }
     }
   }, []);
@@ -657,6 +660,7 @@ export function useClaudeSession() {
     changePermissionMode,
     respondToPermission,
     setError,
-    setMessages
+    setMessages,
+    setCompacting: (value) => setSessionStats(prev => ({ ...prev, isCompacting: value })),
   };
 }