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-testing.md

@@ -1,39 +0,0 @@
----
-description: "Python testing: pytest framework, coverage reporting, test categorization with markers"
-globs: ["**/*.py"]
-alwaysApply: false
----
-
-# Python Testing
-
-> This file extends [common/testing.md](../common/testing.md) with Python specific content.
-
-## Framework
-
-Use **pytest** as the testing framework.
-
-## Coverage
-
-```bash
-pytest --cov=src --cov-report=term-missing
-```
-
-## Test Organization
-
-Use `pytest.mark` for test categorization:
-
-```python
-import pytest
-
-@pytest.mark.unit
-def test_calculate_total():
-    ...
-
-@pytest.mark.integration
-def test_database_connection():
-    ...
-```
-
-## Reference
-
-See skill: `python-testing` for detailed pytest patterns and fixtures.