Add manual update check using GitHub Releases

[DeanJ87]

Summary

Add a manual update check against GitHub Releases.

The app should be able to tell the user whether a newer version is available without implementing automatic download or installation.

Requirements

• Add a manual update check, not a background auto-updater.
• Query the public GitHub Releases API for this repository.
• Compare the current app version with the latest available release.
• Support stable and beta channels:
  • stable ignores GitHub prereleases.
  • beta includes GitHub prereleases.
• Default channel should be stable.
• Expose update status through the web UI and/or a small API endpoint.
• Optionally expose a CLI command such as --check-update.
• Do not download or install updates.
• Do not send SQMeter readings, config values, generated UUIDs, analytics, or usage data.
• Privacy docs must explain that update checks contact GitHub and may expose normal request metadata to GitHub.

Suggested behaviour

For stable channel:

• Use the latest non-prerelease GitHub release.
• Ignore draft releases.
• Ignore prereleases.

For beta channel:

• Include prereleases.
• Ignore draft releases.
• Pick the newest valid semantic version.

Example JSON response:

{
  "current_version": "v0.2.0",
  "latest_version": "v0.2.1",
  "channel": "stable",
  "update_available": true,
  "release_url": "https://github.com/DeanJ87/SQMeter-ASCOM-Alpaca/releases/tag/v0.2.1"
}

Privacy/documentation

Update PRIVACY.md and docs to explain:

• update checks contact GitHub Releases.
• no telemetry is sent.
• no SQMeter readings are sent.
• no config values are sent.
• no device UUID is sent.
• GitHub may receive normal request metadata such as IP address and user agent.

Non-goals

• Do not implement automatic update installation.
• Do not download release assets.
• Do not add background scheduled update checks.
• Do not require a GitHub token.
• Do not fail app startup if GitHub is unavailable.

Validation

• go test ./...
• Unit tests for version comparison:
  • stable newer than current.
  • current equal latest.
  • prerelease ignored on stable.
  • prerelease included on beta.
  • invalid tags ignored.
• Unit tests for GitHub API parsing using mocked HTTP responses.
• Manual dashboard/CLI check if implemented.

Suggested branch

feat/manual-update-check