Add GitHub repository creation link and GitHub integration platform

[Copilot]

Description

Surfaces a direct link to https://github.com/new in the Integrations UI so users can quickly create a GitHub repository for their MyClaw/OpenClaw projects. Also wires up github as a first-class integration platform across the stack.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)

Related Issue(s)

Changes Made

• src/github.js — New GitHub API client matching the openclaw.js pattern: getRepository, createPredictionIssue, syncPrediction, listSyncedPredictions, getCreateRepositoryUrl. Uses correct token auth scheme (not Bearer).
• backend/src/models/Integration.js — Added 'github' to the platform ENUM.
• backend/src/controllers/integrationsController.js — Added GitHub to getPlatforms with description, features, and createRepoUrl: 'https://github.com/new'.
• frontend/src/pages/Integrations.js — Two UI touch points:
  • Header: GitHub-branded "Create GitHub Repository" button linking to https://github.com/new
  • Add Integration modal: inline hint with direct link when GitHub platform is selected

Testing

• Unit tests pass
• Integration tests pass
• Manual testing completed
• No breaking changes

Screenshots (if applicable)

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own 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
• 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
• Any dependent changes have been merged and published

Additional Context

GitHub API requires token <PAT> auth (not Bearer). Set GITHUB_TOKEN in .env to enable API features; the repo creation link works without a token since it's just a redirect to GitHub's UI.