Revert "feat(ecc): prune plugin 43→12 items, promote 7 rules to .claude/rules/ (#245)"

This reverts commit 1bd68ff534.

.cursor/rules/common-testing.md

@@ -0,0 +1,34 @@
+---
+description: "Testing requirements: 80% minimum coverage, TDD workflow, test types"
+alwaysApply: true
+---
+
+# Testing Requirements
+
+## Minimum Test Coverage: 80%
+
+Test Types (ALL required):
+1. **Unit Tests** - Individual functions, utilities, components
+2. **Integration Tests** - API endpoints, database operations
+3. **E2E Tests** - Critical user flows (framework chosen per language)
+
+## Test-Driven Development
+
+MANDATORY workflow:
+1. Write test first (RED)
+2. Run test - it should FAIL
+3. Write minimal implementation (GREEN)
+4. Run test - it should PASS
+5. Refactor (IMPROVE)
+6. Verify coverage (80%+)
+
+## Troubleshooting Test Failures
+
+1. Use **tdd-guide** agent
+2. Check test isolation
+3. Verify mocks are correct
+4. Fix implementation, not tests (unless tests are wrong)
+
+## Agent Support
+
+- **tdd-guide** - Use PROACTIVELY for new features, enforces write-tests-first