Center text horizontally and vertically in bubbles

- Add horizontal centering for each line of text
- Add vertical centering for the entire text block
- Ensure text doesn't overflow the top of the bubble
- Maintain compatibility with both built-in and TTF fonts

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

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

image.php

@@ -336,16 +336,37 @@ if ($currentLine !== '') {
     $lines[] = $currentLine;
 }
 
+// Center text vertically in the bubble
+$lineCount = count($lines);
+if (isset($config['use_builtin_font'])) {
+    $totalTextHeight = $lineCount * imagefontheight(5);
+} else {
+    $totalTextHeight = $lineCount * $config['line_height'];
+}
+
+// Calculate vertical starting position for centered text
+$startY = $textAreaY + ($textAreaHeight - $totalTextHeight) / 2;
+if ($startY < $textAreaY) $startY = $textAreaY; // Ensure text doesn't overflow top
+
 // Draw text
-$y = $textAreaY + $config['font_size']; // Start position for text
+$y = $startY + $config['font_size']; // Start position for centered text
 foreach ($lines as $line) {
     if (isset($config['use_builtin_font'])) {
+        // Calculate width for centering horizontally
+        $lineWidth = imagefontwidth(5) * strlen($line);
+        $x = $textAreaX + ($textAreaWidth - $lineWidth) / 2;
+        
         // Use built-in font (less nice but always available)
-        imagestring($canvas, 5, $textAreaX, $y, $line, $textColor);
+        imagestring($canvas, 5, $x, $y, $line, $textColor);
         $y += imagefontheight(5);
     } else {
+        // Calculate width for centering horizontally
+        $bbox = imagettfbbox($config['font_size'], 0, $config['font'], $line);
+        $lineWidth = $bbox[2] - $bbox[0];
+        $x = $textAreaX + ($textAreaWidth - $lineWidth) / 2;
+        
         // Use TrueType font (nicer but requires font file)
-        imagettftext($canvas, $config['font_size'], 0, $textAreaX, $y, $textColor, $config['font'], $line);
+        imagettftext($canvas, $config['font_size'], 0, $x, $y, $textColor, $config['font'], $line);
         $y += $config['line_height'];
     }
 }