DOC: Add CLAUDE.md shim that delegates to AGENTS.md

[thewtex]

Claude Code expects a CLAUDE.md entrypoint, but this repo already
standardizes on a single root‐level AGENTS.md for all agent
instructions. Note that the new CLAUDE.md is intentionally minimal and
just forwards Claude to AGENTS.md (via an explicit reference) so that:

• AGENTS.md remains the canonical, editor‑agnostic source of truth
• Claude Code and other CLAUDE.md‑aware tools still "just work"
• We avoid fragile symlink hacks and keep behavior consistent across platforms and CLIs

[greptile-apps]

Greptile Summary

This PR adds a minimal CLAUDE.md shim at the repository root so that Claude Code (which looks for CLAUDE.md on start-up) immediately delegates to the already-existing, canonical AGENTS.md. The single @AGENTS.md directive uses Claude Code's native file-import syntax to pull in the full agent guide without duplicating content.

• The @AGENTS.md include syntax is correct for Claude Code's CLAUDE.md resolution; Claude Code will read and merge the referenced file at load time.
• AGENTS.md exists at the repo root and contains comprehensive guidance, so the delegation target is valid.
• The approach avoids symlinks, duplication, and platform-specific fragility while keeping AGENTS.md as the single source of truth for all agent tooling.

Confidence Score: 5/5

• This PR is safe to merge — it is a documentation-only addition with no code changes.
• The change consists of five lines of Markdown in a new file. The @AGENTS.md syntax is the documented Claude Code mechanism for including additional context files, AGENTS.md already exists and is well-formed, and the PR introduces no risk to any compiled or runtime artifact.
• No files require special attention.

Important Files Changed

Filename	Overview
CLAUDE.md	Adds a minimal Claude Code entrypoint that delegates to the canonical AGENTS.md via the @AGENTS.md file-import syntax; no logic, no code — documentation only.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A([Claude Code starts]) --> B{Is there a CLAUDE.md\nat repo root?}
    B -- Yes --> C[Load CLAUDE.md]
    C --> D["Encounter @AGENTS.md\ndirective"]
    D --> E[Load & merge AGENTS.md\ninto active context]
    E --> F([Full ITK agent context\navailable to Claude])
    B -- No --> G([No project context\nloaded])

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