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/commands/test-coverage.md

@@ -1,27 +0,0 @@
-# Test Coverage
-
-Analyze test coverage and generate missing tests:
-
-1. Run tests with coverage: npm test --coverage or pnpm test --coverage
-
-2. Analyze coverage report (coverage/coverage-summary.json)
-
-3. Identify files below 80% coverage threshold
-
-4. For each under-covered file:
-   - Analyze untested code paths
-   - Generate unit tests for functions
-   - Generate integration tests for APIs
-   - Generate E2E tests for critical flows
-
-5. Verify new tests pass
-
-6. Show before/after coverage metrics
-
-7. Ensure project reaches 80%+ overall coverage
-
-Focus on:
-- Happy path scenarios
-- Error handling
-- Edge cases (null, undefined, empty)
-- Boundary conditions