feat: add v3 character card support

- Added CharacterCardV3 struct to handle v3 format
- Created From<CharacterCardV3> for CharacterCardV2Data conversion
- Updated read_character_card_from_png() to detect and parse both v2 and v3 specs
- V3 cards have top-level fields + nested data object
- Maintains full backward compatibility with v2 cards
- Export still uses v2 format for maximum compatibility

check_png_chunks.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+import struct
+import sys
+
+def read_png_chunks(filename):
+    with open(filename, 'rb') as f:
+        # Check PNG signature
+        signature = f.read(8)
+        if signature != b'\x89PNG\r\n\x1a\n':
+            print("Not a valid PNG file!")
+            return
+        
+        print("Valid PNG file")
+        print("\nChunks found:")
+        print("-" * 60)
+        
+        chunk_num = 0
+        while True:
+            # Read chunk length
+            length_data = f.read(4)
+            if len(length_data) < 4:
+                break
+            
+            length = struct.unpack('>I', length_data)[0]
+            
+            # Read chunk type
+            chunk_type = f.read(4)
+            if len(chunk_type) < 4:
+                break
+            
+            chunk_type_str = chunk_type.decode('ascii', errors='ignore')
+            
+            # Read chunk data
+            data = f.read(length)
+            
+            # Read CRC
+            crc = f.read(4)
+            
+            chunk_num += 1
+            
+            # Print chunk info
+            print(f"{chunk_num}. Type: {chunk_type_str:8s} | Length: {length:8d} bytes", end='')
+            
+            # For text chunks, show the keyword
+            if chunk_type_str in ['tEXt', 'iTXt', 'zTXt']:
+                try:
+                    # Find null terminator for keyword
+                    null_pos = data.find(b'\x00')
+                    if null_pos > 0:
+                        keyword = data[:null_pos].decode('latin-1', errors='ignore')
+                        print(f" | Keyword: '{keyword}'", end='')
+                        
+                        # For tEXt, show some of the text content
+                        if chunk_type_str == 'tEXt' and len(data) > null_pos + 1:
+                            text_preview = data[null_pos+1:null_pos+51]
+                            print(f" | Text: {text_preview[:50]}...", end='')
+                except:
+                    pass
+            
+            print()
+            
+            if chunk_type_str == 'IEND':
+                break
+        
+        print("-" * 60)
+        print(f"Total chunks: {chunk_num}")
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        print("Usage: check_png_chunks.py <png_file>")
+        sys.exit(1)
+    
+    read_png_chunks(sys.argv[1])