[task] Add current scaffold command output examples

[phongndo]

Area

Docs

Goal

Document the current scaffold command output that a first-time contributor can run locally.

Why this matters

Students should be able to confirm that their clone works without mistaking placeholder output for finished product behavior.

Relevant files

• README.md
• docs/onboarding.md
• docs/development.md

Depends on

None. This can be claimed immediately.

Out of scope

• Do not implement new CLI, TUI, desktop, Git, or GitHub behavior.
• Do not present placeholder output as a finished feature.
• Do not add screenshots unless they are clearly labeled as scaffold screenshots.

Definition of done

• Docs show expected output or output shape for the current scaffold commands.
• Examples include at least two of nexgit version --json, nexgit repo status --json, nexgit stack list --json, or the app-server system.version smoke test.
• The wording says clearly which outputs are placeholder scaffold behavior.
• Existing setup instructions remain intact.

Verification

• pnpm format:prettier:check
• Manually run the documented commands and include the commands used in the PR description.

Contributor notes

This is a good first issue. The main job is accuracy and clear wording, not adding product behavior.

[AdventureKO]

/claim