Add debug logging to signal handling and cleanup system

- Add debug logs when cleanup handlers are registered
- Add debug logs in signal handler showing registered handler count
- Add debug logs during cleanup execution showing each handler call
- Improve error logging with handler index information

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

Co-Authored-By: Claude <[email protected]>

Author: namespacebrian

src/Terminus.php

@@ -566,6 +566,7 @@ private function setupSignalHandlers(): void
     public function handleSignal(int $signal): void
     {
         $this->logger->notice('Received signal {signal}, performing cleanup...', ['signal' => $signal]);
+        $this->logger->debug('Signal handler called with {count} cleanup handlers registered', ['count' => count($this->cleanup_handlers)]);
 
         $this->cleanup();
 
@@ -592,6 +593,7 @@ public static function getInstance(): ?self
     public function registerCleanupHandler(callable $handler): void
     {
         $this->cleanup_handlers[] = $handler;
+        $this->logger->debug('Cleanup handler registered. Total handlers: {count}', ['count' => count($this->cleanup_handlers)]);
     }
 
     /**
@@ -600,12 +602,16 @@ public function registerCleanupHandler(callable $handler): void
     private function cleanup(): void
     {
         try {
+            $this->logger->debug('Starting cleanup with {count} handlers', ['count' => count($this->cleanup_handlers)]);
+
             // Call all registered cleanup handlers
-            foreach ($this->cleanup_handlers as $handler) {
+            foreach ($this->cleanup_handlers as $index => $handler) {
                 try {
+                    $this->logger->debug('Calling cleanup handler {index}', ['index' => $index]);
                     call_user_func($handler);
+                    $this->logger->debug('Cleanup handler {index} completed successfully', ['index' => $index]);
                 } catch (\Exception $e) {
-                    $this->logger->error('Error in cleanup handler: {message}', ['message' => $e->getMessage()]);
+                    $this->logger->error('Error in cleanup handler {index}: {message}', ['index' => $index, 'message' => $e->getMessage()]);
                 }
             }