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/common-hooks.md

@@ -0,0 +1,34 @@
+---
+description: "Hooks system: types, auto-accept permissions, TodoWrite best practices"
+alwaysApply: true
+---
+# Hooks System
+
+## Hook Types
+
+- **PreToolUse**: Before tool execution (validation, parameter modification)
+- **PostToolUse**: After tool execution (auto-format, checks)
+- **Stop**: When session ends (final verification)
+
+## Auto-Accept Permissions
+
+Use with caution:
+- Enable for trusted, well-defined plans
+- Disable for exploratory work
+- Never use dangerously-skip-permissions flag
+- Configure `allowedTools` in `~/.claude.json` instead
+
+## TodoWrite Best Practices
+
+Use TodoWrite tool to:
+- Track progress on multi-step tasks
+- Verify understanding of instructions
+- Enable real-time steering
+- Show granular implementation steps
+
+Todo list reveals:
+- Out of order steps
+- Missing items
+- Extra unnecessary items
+- Wrong granularity
+- Misinterpreted requirements