feat: Implement app versioning and update gitignore

- Adds appVersion and buildNumber to AppConfig.swift for centralized version management.
- Updates scryfallUserAgent to use the dynamic appVersion.
- Updates .gitignore to exclude AI asset and training directories.
- Adds a version check step to the README release checklist.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -27,3 +27,10 @@ env/
 
 # Mac-specific
 .DS_Store
+
+# AI-generated assets
+Raw_Assets/
+Ready_Assets/
+
+# ML Training Data
+IYmtg_Training/