Fix the CLAUDE.md import shim

Andrew Dunnrequested to merge
fix/claude-md-import into main

The old @import AGENTS.md line loaded nothing and suppressed the native AGENTS.md fallback; @AGENTS.md is the documented import. This fixes the five CLAUDE.md templates, the lab template page, and names the shim line in the agents-md standard so new repos inherit the working form.

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