feat: Add dynamic slash commands from Claude with UI improvements

- Load available commands from Claude at session start (control_initialized event)
- Display commands in autocomplete dropdown with search in name and description
- Group commands into "UI Commands" and "Claude Commands" sections
- Shorten display names by removing common prefixes (taches-cc-resources:, claude-mem:)
- Blacklist TUI-only commands (vim, terminal-setup, ide, etc.)
- Add max-height with scrollbar for long command lists
- Implement auto-scroll to keep selected command visible during keyboard navigation

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

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

frontend/src/contexts/SessionContext.jsx

@@ -38,6 +38,7 @@ function createSessionState(id, host = 'neko', project = '/home/sumdex/projects'
     },
     permissionMode: 'default',
     controlInitialized: false,
+    availableCommands: [], // Slash commands from Claude
     pendingPermission: null,
     unreadCount: 0,
     currentContext: null, // For dynamic tab naming
@@ -156,11 +157,12 @@ export function SessionProvider({ children }) {
   const updateSession = useCallback((sessionId, updates) => {
     setSessions(prev => {
       if (!prev[sessionId]) return prev;
+      const newUpdates = typeof updates === 'function' ? updates(prev[sessionId]) : updates;
       return {
         ...prev,
         [sessionId]: {
           ...prev[sessionId],
-          ...(typeof updates === 'function' ? updates(prev[sessionId]) : updates),
+          ...newUpdates,
         },
       };
     });
@@ -444,6 +446,7 @@ export function SessionProvider({ children }) {
       case 'control_initialized': {
         updateSession(sessionId, {
           controlInitialized: true,
+          availableCommands: data.commands || [],
         });
         // Restore saved permission mode after control is initialized
         // Read from localStorage since sessions state may be stale in this callback