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-security.md

@@ -1,34 +0,0 @@
----
-description: "Mandatory security checks, secret management, and security response protocol"
-alwaysApply: true
----
-
-# Security Guidelines
-
-## Mandatory Security Checks
-
-Before ANY commit:
-- [ ] No hardcoded secrets (API keys, passwords, tokens)
-- [ ] All user inputs validated
-- [ ] SQL injection prevention (parameterized queries)
-- [ ] XSS prevention (sanitized HTML)
-- [ ] CSRF protection enabled
-- [ ] Authentication/authorization verified
-- [ ] Rate limiting on all endpoints
-- [ ] Error messages don't leak sensitive data
-
-## Secret Management
-
-- NEVER hardcode secrets in source code
-- ALWAYS use environment variables or a secret manager
-- Validate that required secrets are present at startup
-- Rotate any secrets that may have been exposed
-
-## Security Response Protocol
-
-If security issue found:
-1. STOP immediately
-2. Use **security-reviewer** agent
-3. Fix CRITICAL issues before continuing
-4. Rotate any exposed secrets
-5. Review entire codebase for similar issues