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

password_validator/README.md

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+# Feature A — Password Validator
+
+## Your goal
+
+Implement `PasswordValidator` using strict TDD. **Do not write any production code before you have a failing test.**
+
+## Rules to implement (in order)
+
+| Step | Rule | Error message |
+|------|------|---------------|
+| 1 | At least 8 characters long | `Must be at least 8 characters long` |
+| 2 | At least one uppercase letter (A–Z) | `Must contain at least one uppercase letter` |
+| 3 | At least one digit (0–9) | `Must contain at least one digit` |
+| 4 | At least one special character (`!@#$%^&*`) | `Must contain at least one special character (!@#$%^&*)` |
+| 5 | No spaces | `Must not contain spaces` |
+| 6 | All errors reported at once (refactor) | — |
+
+## The rhythm — repeat for every rule
+
+```
+1. Uncomment the next test → run → watch it FAIL (Red)
+2. Write the minimum code to make it pass → run → GREEN
+3. Refactor if needed → run → still GREEN
+4. Move to the next test
+```
+
+## Running the tests
+
+```bash
+dart pub get
+dart test
+```
+
+## Files
+
+- `lib/password_validator.dart` — your implementation goes here
+- `test/password_validator_test.dart` — uncomment tests one at a time
+
+## Hint for Step 6 (the refactor insight)
+
+Once all 5 rules pass, you'll likely have 5 separate `if` blocks in `validate()`.
+Think about how to represent each rule as **data** instead of **code**.
+What if each rule were just a function in a list?