Polish dashboard empty-state copy

[lpc0387]

6. Polish dashboard empty-state copy

Labels: good first issue, ui polish, dashboard

Body:

When the dashboard has no runs, logs, lessons, or workers to show, the empty-state text should help new users understand what to do next. Review the dashboard HTML and improve one or two empty states with clearer copy that points to the sandbox or CLI quick start.

Suggested scope:

• Keep the change limited to static copy in the dashboard UI.
• Do not redesign layout, colors, or data fetching in the same PR.
• Keep wording concise and consistent with the local-first safety boundary.
• If both web/index.html and sandbox/index.html share the same copy, keep them aligned.

Acceptance criteria:

• At least one confusing or generic empty state is replaced with actionable text.
• The copy does not imply the sandbox uses production data or real workers by default.
• If mirrored dashboard files are updated, the same user-facing copy appears in each relevant file.
• Verification notes include manual browser or static review; no full test suite is required.

Why it is newcomer-friendly:

This is a small UI writing task. It is easy to review visually and does not require changing dashboard APIs.

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This issue was created from the v5.0 launch backlog in docs/launch/good-first-issues.md.