Scan Dashboard: update empty state copy to explain what was scanned

[Initsogar]

Fixes DOTMSD-670

Proposed Changes

• Updated the Scan empty state description from "everything looked great" to "found no security issues"

Why are these changes being made?

The previous empty state copy (“everything looked great”) was too vague and didn't help users understand what Scan actually does or what was checked. This change makes it clearer that Scan is actively checking for security issues, helping users understand the value of the feature even when no threats are found.

Testing Instructions

1. Navigate to a site's Scan page that has no active threats: /v2/sites/{site}/scan
2. Verify the empty state shows: "The last scan ran [time] ago and found no security issues."
3. Compare with the before/after screenshots shared below

Before	After

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-160360

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-160360&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-160360&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug dotmsd-670-scan-more-meaningful-copy-for-the-empty-state on your sandbox.