chore: set default output format to JPG, add .gitignore

- config.ini: output_format = jpg (quality 95)
- .gitignore: exclude build/, output/, IDE files

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

.gitignore

@@ -0,0 +1,15 @@
+# Build
+build/
+
+# Output images
+output/
+
+# IDE
+.vscode/
+.idea/
+*.user
+
+# Compiled
+*.o
+*.a
+*.so