Initial commit: Complete TDD workshop materials

- Workshop documentation (WORKSHOP_PLAN, FACILITATOR_GUIDE, etc.)
- FizzBuzz kata with demo script (git history to be recreated)
- Password Validator kata with demo script and solution
- Shopping Cart kata with demo script and solution
- Setup guide and TDD reference card for participants

.gitignore

@@ -0,0 +1,18 @@
+# Dart build artifacts
+.dart_tool/
+.packages
+pubspec.lock
+build/
+
+# IDE
+.idea/
+.vscode/
+*.iml
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Temporary files
+*.log
+*.tmp