Add github.dev (VS Code Online) snippet per repository

[maraf]

Closes #112

Adds a quick jump into the web-based VS Code editor for every GitHub repository surfaced by the provider, so users can open a repo in github.dev without manually rewriting the URL.

Approach

Extend GitHubSnippetProvider.AddSnippetsForRepository with one additional low-priority SnippetModel:

• Title: {repositoryTitle} - VS Code Online
• URL: https://github.dev/{owner}/{repository}

Because every repository source (user repos, organization repos, starred repos, and ExtraRepositories) funnels through AddSnippetsForRepository, the new snippet is emitted uniformly with no changes to the individual code paths or configuration.

Notes

• No new configuration flag: the link applies to any GitHub repo and has no runtime cost.
• Title wording matches the issue phrasing ("vscode online") and sits alongside the existing sub-entries (Issues, Pulls, Find file, Code search, My activity).

[Copilot]

Pull request overview

Adds a new per-repository snippet that opens the repository directly in the web-based VS Code editor (github.dev), making it easy for users to jump into editing without rewriting URLs.

Changes:

• Extend GitHubSnippetProvider.AddSnippetsForRepository to emit an additional low-priority snippet.
• New snippet title format: {repositoryTitle} - VS Code Online.
• New snippet URL format: https://github.dev/{owner}/{repository}.

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