[task] Review first-run copy for local GitHub workflow client

[phongndo]

Goal

Review and improve first-run copy so the desktop app clearly presents Nexgit as a local GitHub workflow client.

Why this matters

The first screen should not imply Nexgit is a stacked-diff clone, a generic Git GUI, or a finished product. It should honestly explain the pre-alpha GitHub workflow dashboard direction.

Command/API target

Design/comment-only issue. A code PR is optional.

Depends on

• [task] Render GitHub workflow dashboard in desktop #14 for the first desktop dashboard direction, though design notes can start earlier.

Out of scope

• Do not redesign the whole desktop app.
• Do not implement app-server GitHub methods.
• Do not add stacked PR messaging.

Definition of done

• The contribution includes UX notes, proposed copy, screenshots, or a small copy/doc update.
• The proposal explains what a first-time user should understand after opening the app.
• The copy references GitHub workflow state: issues, PRs, checks, reviews, or maintainer queue.

Verification

• Attach screenshots, a Figma link, or written UX notes.
• If changing docs or copy in the repo, run pnpm format:prettier:check.

Contributor notes

This is a good first design issue. A useful contribution can be only a comment with screenshots and proposed copy.