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/python-security.md

@@ -1,31 +0,0 @@
----
-description: "Python security: dotenv secret management, bandit static analysis"
-globs: ["**/*.py"]
-alwaysApply: false
----
-
-# Python Security
-
-> This file extends [common/security.md](../common/security.md) with Python specific content.
-
-## Secret Management
-
-```python
-import os
-from dotenv import load_dotenv
-
-load_dotenv()
-
-api_key = os.environ["OPENAI_API_KEY"]  # Raises KeyError if missing
-```
-
-## Security Scanning
-
-- Use **bandit** for static security analysis:
-  ```bash
-  bandit -r src/
-  ```
-
-## Reference
-
-See skill: `django-security` for Django-specific security guidelines (if applicable).