feat: add Cursor, Codex, and OpenCode harnesses — maximize every AI coding tool

- AGENTS.md: universal cross-tool file read by Claude Code, Cursor, Codex, and OpenCode
- .cursor/: 15 hook events via hooks.json, 16 hook scripts with DRY adapter pattern,
  29 rules (9 common + 20 language-specific) with Cursor YAML frontmatter
- .codex/: reference config.toml, Codex-specific AGENTS.md supplement,
  10 skills ported to .agents/skills/ with openai.yaml metadata
- .opencode/: 3 new tools (format-code, lint-check, git-summary), 3 new hooks
  (shell.env, experimental.session.compacting, permission.ask), expanded instructions,
  version bumped to 1.6.0
- README: fixed Cursor section, added Codex section, added cross-tool parity table
- install.sh: now copies hooks.json + hooks/ for --target cursor

.cursor/rules/python-patterns.md

@@ -0,0 +1,39 @@
+---
+description: "Python patterns extending common rules"
+globs: ["**/*.py", "**/*.pyi"]
+alwaysApply: false
+---
+# Python Patterns
+
+> This file extends the common patterns rule with Python specific content.
+
+## Protocol (Duck Typing)
+
+```python
+from typing import Protocol
+
+class Repository(Protocol):
+    def find_by_id(self, id: str) -> dict | None: ...
+    def save(self, entity: dict) -> dict: ...
+```
+
+## Dataclasses as DTOs
+
+```python
+from dataclasses import dataclass
+
+@dataclass
+class CreateUserRequest:
+    name: str
+    email: str
+    age: int | None = None
+```
+
+## Context Managers & Generators
+
+- Use context managers (`with` statement) for resource management
+- Use generators for lazy evaluation and memory-efficient iteration
+
+## Reference
+
+See skill: `python-patterns` for comprehensive patterns including decorators, concurrency, and package organization.