Add AGENTS.md for tool-agnostic agent instructions with CLAUDE.md symlink

AGENTS.md points agents to .ai/skills/ for skill discovery. CLAUDE.md
symlinks to it so Claude Code picks it up as project instructions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

AGENTS.md

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+# Agent Instructions
+
+This project uses AI agent skills stored in `.ai/skills/`. Each skill is a directory containing a `SKILL.md` file with instructions for performing a specific task.
+
+Skills follow the [Agent Skills](https://agentskills.io) open standard. Each skill directory contains:
+
+- `SKILL.md` — The skill definition with YAML frontmatter (name, description, argument-hint) and detailed instructions.
+- Additional supporting files as needed.

CLAUDE.md

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+AGENTS.md