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-git-workflow.md

@@ -0,0 +1,28 @@
+---
+description: "Git workflow: conventional commits, PR process"
+alwaysApply: true
+---
+# Git Workflow
+
+## Commit Message Format
+```
+<type>: <description>
+
+<optional body>
+```
+
+Types: feat, fix, refactor, docs, test, chore, perf, ci
+
+Note: Attribution disabled globally via ~/.claude/settings.json.
+
+## Pull Request Workflow
+
+When creating PRs:
+1. Analyze full commit history (not just latest commit)
+2. Use `git diff [base-branch]...HEAD` to see all changes
+3. Draft comprehensive PR summary
+4. Include test plan with TODOs
+5. Push with `-u` flag if new branch
+
+> For the full development process (planning, TDD, code review) before git operations,
+> see the development workflow rule.