feat: Add TDD code generation workflow as optional path

Add Test-Driven Development (TDD) as a selectable code generation
strategy in the Construction phase. Users can now choose between
TDD and standard approaches before code generation begins.

Changes:
- Add tdd-code-generation.md with full TDD workflow (Red-Green-Refactor)
- Add TDD selection prompt (Step 0) in core-workflow.md
- Add TDD artifact detection in build-and-test.md

Validation:
- Internal large-scale TTT conducted comparing TDD vs Standard paths.
  Teams using TDD completed development in significantly less time
  with more complete results (100% improvement).
- Field feedback confirmed that TDD-based AI-DLC runs produced
  finished outputs in a single pass or with minimal issues.
- Stability verified through multiple customer 1-day workshops
  with consistent, reliable results.

Co-authored-by: Jeongho Han <[email protected]>
Co-authored-by: Hyojin Jung <[email protected]>

Author: 3 people

aidlc-rules/aws-aidlc-rule-details/construction/build-and-test.md

@@ -9,10 +9,30 @@
 
 ---
 
+## Step 0: Detect TDD Artifacts (MANDATORY)
+
+**Check for TDD artifacts** in `aidlc-docs/construction/plans/`:
+- Look for `{unit-name}-test-plan.md` files
+- Look for `{unit-name}-contracts.md` files
+
+**If TDD artifacts found**:
+- TDD was used for code generation
+- Unit tests already executed and passed (🟢 status in test-plan.md)
+- Load test results from `{unit-name}-test-plan.md`
+- Skip re-running unit tests that are already 🟢 Passed
+- Focus on integration tests and other test types
+
+**If NO TDD artifacts found**:
+- Standard code generation was used
+- Proceed with full test execution
+
+---
+
 ## Step 1: Analyze Testing Requirements
 
 Analyze the project to determine appropriate testing strategy:
 - **Unit tests**: Already generated per unit during code generation
+  - **If TDD**: Already executed and passed - verify only
 - **Integration tests**: Test interactions between units/services
 - **Performance tests**: Load, stress, and scalability testing
 - **End-to-end tests**: Complete user workflows
@@ -81,6 +101,14 @@ Create `aidlc-docs/construction/build-and-test/unit-test-instructions.md`:
 
 ## Run Unit Tests
 
+**If TDD was used** (test-plan.md exists):
+- Unit tests already executed during Code Generation
+- All tests should be 🟢 Passed in `{unit-name}-test-plan.md`
+- Run verification only to confirm tests still pass after any final changes
+
+**If Standard code generation was used**:
+- Execute full unit test suite
+
 ### 1. Execute All Unit Tests
 \`\`\`bash
 [Command to run all unit tests]