feat: add backend version update checking

[Copilot]

Implements backend logic to check for new releases and expose the result via a REST endpoint, enabling the UI to surface update notifications.

Changes

src/utils/VersionChecker.js (new utility class)

• getCurrentVersion() — reads from VERSION env var (Docker build-time injection) or package.json
• fetchTags() — queries GitHub Tags API, filters to v* tags (excludes previews), sorts descending
• checkDockerImageExists(tag) — probes GHCR manifest endpoint with OAuth token flow to confirm image availability
• checkForUpdates() — returns { current, latest, hasUpdate, releaseUrl }, only surfaces a newer version if its Docker image is already published

src/routes/StatusRoutes.js

• Adds GET /api/version/check (auth-required)
• Respects CHECK_UPDATE=false env var; returns { disabled: true } without hitting GitHub

Configuration

• .env.example documents CHECK_UPDATE=true
• README.md / README_EN.md updated with env variable table entry

UI integration (ui/app/pages/StatusPage.vue)

• Calls /api/version/check on page load; renders update badge with release link when hasUpdate is true

// Example response when update is available
{
  current: "0.7.0",
  latest: "v0.7.1",
  hasUpdate: true,
  releaseUrl: "https://github.com/iBUHub/AIStudioToAPI/releases/tag/v0.7.1"
}

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