docs: add AGENTS.md redirecting to CLAUDE.md

Provides a standard entry point for non-Claude AI coding agents
(Codex, Copilot, Cursor, etc.) that look for AGENTS.md, directing
them to follow the project rules in CLAUDE.md. Also references
.claude/ for subagent, skill, and orchestration script definitions.

Co-Authored-By: Claude <claude@anthropic.com>

AGENTS.md

@@ -0,0 +1,13 @@
+# AGENTS.md
+
+All project instructions, conventions, and development guidelines are maintained in [CLAUDE.md](CLAUDE.md).
+
+Strictly follow the rules defined there.
+
+## Project Tooling
+
+Subagent definitions, skills, and orchestration scripts live in [`.claude/`](.claude/):
+
+- `.claude/agents/` - Specialized subagent definitions for the Task tool
+- `.claude/skills/` - User-invocable skills (slash commands)
+- `.claude/scripts/` - Orchestration scripts that chain multiple Claude CLI calls