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/golang-hooks.md

@@ -0,0 +1,16 @@
+---
+description: "Go hooks extending common rules"
+globs: ["**/*.go", "**/go.mod", "**/go.sum"]
+alwaysApply: false
+---
+# Go Hooks
+
+> This file extends the common hooks rule with Go specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **gofmt/goimports**: Auto-format `.go` files after edit
+- **go vet**: Run static analysis after editing `.go` files
+- **staticcheck**: Run extended static checks on modified packages