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/refactor-clean.md

@@ -1,28 +0,0 @@
-# Refactor Clean
-
-Safely identify and remove dead code with test verification:
-
-1. Run dead code analysis tools:
-   - knip: Find unused exports and files
-   - depcheck: Find unused dependencies
-   - ts-prune: Find unused TypeScript exports
-
-2. Generate comprehensive report in .reports/dead-code-analysis.md
-
-3. Categorize findings by severity:
-   - SAFE: Test files, unused utilities
-   - CAUTION: API routes, components
-   - DANGER: Config files, main entry points
-
-4. Propose safe deletions only
-
-5. Before each deletion:
-   - Run full test suite
-   - Verify tests pass
-   - Apply change
-   - Re-run tests
-   - Rollback if tests fail
-
-6. Show summary of cleaned items
-
-Never delete code without running tests first!