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>

backend/server.js

@@ -806,6 +806,7 @@ wss.on('connection', async (ws, req) => {
                   if (pending.type === 'initialize') {
                     isInitialized = true;
                     console.log(`[${sessionId}] Control protocol initialized`);
+                    console.log(`[${sessionId}] Available commands:`, JSON.stringify(response.response?.commands, null, 2));
                     // Send available commands/models to frontend
                     sendToClient('control_initialized', {
                       commands: response.response?.commands,