docs: update stale dep-lockstep bullet and npm test annotation (#4924)

[AbhiPra24]

Closes #4924

Description

This updates two stale statements in AGENTS.md:

1. In Development setup, updates npm test -w src/<server> annotation from (vitest, with coverage) to (vitest). Each workspace's test script runs vitest run, while coverage is handled separately by vitest run --coverage.
2. In Dependencies, updates the shared devDependency bullet from Their ranges already differ; do not widen the skew to state that verify:dep-lockstep enforces one identical range everywhere across tracked manifests.

Types of changes

• Documentation update

Checklist

• My code follows the repository's style guidelines
• I have read the MCP Protocol Documentation

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Latest commit: e3c7c40

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