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-security.md

@@ -0,0 +1,31 @@
+---
+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).