fix(setup-helper): add GitHub API fallback for plugin fetches

[qin-ctx]

Description

Improve the OpenClaw setup helper so plugin manifest lookup and plugin file downloads no longer depend solely on raw.githubusercontent.com.

Related Issue

Fixes #1150

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
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• add shared helpers for GitHub raw fetches, GitHub Contents API fallback, and timeout handling in the setup helper
• use the fallback path when resolving plugin manifests, probing plugin directories, and reading fallback package metadata
• route plugin file downloads through the same fallback so installs can continue when raw.githubusercontent.com is blocked but GitHub API access still works

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Manual checks:

• node --check examples/openclaw-plugin/setup-helper/install.js
• verified that v0.3.2 contains examples/openclaw-plugin/install-manifest.json and index.ts, so the reported failure is due to remote file access rather than a missing tag asset

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

This keeps the failure mode explicit: the helper warns when raw.githubusercontent.com is unavailable and only succeeds if the same file can be fetched via the GitHub Contents API. A new npm release of openclaw-openviking-setup-helper is still required before ov-install users receive the fix.

[github-actions]

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