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

ECC community plugin pruning: removed 530+ non-essential files
(.cursor/, .opencode/, docs/ja-JP, docs/zh-CN, docs/zh-TW,
language-specific skills/agents/rules). Retained 4 agents,
3 commands, 5 skills. Promoted 13 rule files (8 common + 5
typescript) to .claude/rules/ for CC native loading. Extracted
reusable patterns to EXTRACTED-PATTERNS.md.

.cursor/rules/common-testing.md

@@ -1,34 +0,0 @@
----
-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