feat: add Cursor IDE support with pre-translated configs

Add complete .cursor/ directory with rules, agents, skills, commands,
and MCP config adapted for Cursor's format. This makes ecc-universal
a truly cross-IDE package supporting Claude Code, Cursor, and OpenCode.

- 27 rule files with YAML frontmatter (description, globs, alwaysApply)
- 13 agent files with full model IDs and readonly flags
- 30 skill directories (identical Agent Skills standard, no translation)
- 31 command files (5 multi-* stubbed for missing codeagent-wrapper)
- MCP config with Cursor env interpolation syntax
- README.md and MIGRATION.md documentation
- install.sh --target cursor flag for project-scoped installation
- package.json updated with .cursor/ in files and cursor keywords

.cursor/rules/python-testing.md

@@ -0,0 +1,39 @@
+---
+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.