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-coding-style.md

@@ -0,0 +1,43 @@
+---
+description: "Python coding style: PEP 8, type annotations, frozen dataclasses, black/isort/ruff formatting"
+globs: ["**/*.py"]
+alwaysApply: false
+---
+
+# Python Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with Python specific content.
+
+## Standards
+
+- Follow **PEP 8** conventions
+- Use **type annotations** on all function signatures
+
+## Immutability
+
+Prefer immutable data structures:
+
+```python
+from dataclasses import dataclass
+
+@dataclass(frozen=True)
+class User:
+    name: str
+    email: str
+
+from typing import NamedTuple
+
+class Point(NamedTuple):
+    x: float
+    y: float
+```
+
+## Formatting
+
+- **black** for code formatting
+- **isort** for import sorting
+- **ruff** for linting
+
+## Reference
+
+See skill: `python-patterns` for comprehensive Python idioms and patterns.