Fix npm fallback for Parallel search plugin install

[Angnuo (angnuoli)]

Description

Fixes Parallel web search plugin installation on networks where the configured npm registry fails TLS negotiation. The installer now retries through reachable registry candidates instead of repeating the same blocked mirror.

Related Issue

N/A

Changes

• Add the Microsoft package feed proxy to npm registry fallback candidates.
• Reuse retryable npm registry error detection for OpenClaw and plugin installs.
• Probe reachable registries and set npm_config_registry per Parallel plugin attempt.
• Add regression coverage for TLS failure fallback and registry propagation.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• CI/CD or build configuration change
• Refactoring (no functional changes)

Testing

• Tests pass locally (cd desktop && npm run test)
• Renderer tests pass locally (cd desktop/renderer && npm run test)
• Build succeeds (powershell -ExecutionPolicy Bypass -File build.ps1)
• Manual testing performed (describe below)

Verified the Parallel plugin installs and loads through https://packagefeedproxy.microsoft.io/npm/ after npmmirror TLS handshake failures. All 106 tests.test_windows_setup_upgrade tests pass.

Checklist

• My code follows the coding guidelines of this project
• I have performed a self-review of my code
• I have commented my code where necessary
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes