Reorder npm diagnostic checks: project-specific before environment

[Copilot]

Addresses feedback from PR #139 to improve diagnostic check ordering in NodePackageManager::diagnoseAndReportNpmFailure().

Changes

• Reordered diagnostic checks to run package.json validation first, before npm/node availability checks
• Updated check numbering in comments to reflect new order

Rationale

Sequential early-return diagnostics should check project-specific issues before environment issues:

Before:

1. npm availability
2. node availability
3. package.json validity

After:

1. package.json validity (quickest, most specific)
2. npm availability
3. node availability

This prevents the inefficient troubleshooting loop where users fix npm installation → re-run → then discover invalid package.json.

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[Copilot]

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[Copilot]

Pull request overview

This PR updates MageForge’s npm-install failure diagnostics to prioritize project-specific validation before environment checks, improving troubleshooting flow in NodePackageManager::diagnoseAndReportNpmFailure().

Changes:

• Moved package.json validity checking to the top of the diagnostic sequence (early return).
• Shifted npm/node availability checks to run after package.json validation.
• Renumbered the “Check N:” comments to match the new order.