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

.claude/settings.local.json

@@ -14,7 +14,8 @@
       "Bash(npm run tauri:dev:*)",
       "Bash(git add:*)",
       "Bash(git commit:*)",
-      "WebSearch"
+      "WebSearch",
+      "Bash(python3:*)"
     ],
     "deny": [],
     "ask": []