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-agents.md

@@ -0,0 +1,53 @@
+---
+description: "Agent orchestration: available agents, parallel execution, multi-perspective analysis"
+alwaysApply: true
+---
+# Agent Orchestration
+
+## Available Agents
+
+Located in `~/.claude/agents/`:
+
+| Agent | Purpose | When to Use |
+|-------|---------|-------------|
+| planner | Implementation planning | Complex features, refactoring |
+| architect | System design | Architectural decisions |
+| tdd-guide | Test-driven development | New features, bug fixes |
+| code-reviewer | Code review | After writing code |
+| security-reviewer | Security analysis | Before commits |
+| build-error-resolver | Fix build errors | When build fails |
+| e2e-runner | E2E testing | Critical user flows |
+| refactor-cleaner | Dead code cleanup | Code maintenance |
+| doc-updater | Documentation | Updating docs |
+
+## Immediate Agent Usage
+
+No user prompt needed:
+1. Complex feature requests - Use **planner** agent
+2. Code just written/modified - Use **code-reviewer** agent
+3. Bug fix or new feature - Use **tdd-guide** agent
+4. Architectural decision - Use **architect** agent
+
+## Parallel Task Execution
+
+ALWAYS use parallel Task execution for independent operations:
+
+```markdown
+# GOOD: Parallel execution
+Launch 3 agents in parallel:
+1. Agent 1: Security analysis of auth module
+2. Agent 2: Performance review of cache system
+3. Agent 3: Type checking of utilities
+
+# BAD: Sequential when unnecessary
+First agent 1, then agent 2, then agent 3
+```
+
+## Multi-Perspective Analysis
+
+For complex problems, use split role sub-agents:
+- Factual reviewer
+- Senior engineer
+- Security expert
+- Consistency reviewer
+- Redundancy checker