Add warning when sitemap is missing or has insufficient URLs

[jjroelofs]

Summary

Add a warning message when the sitemap is unavailable or contains fewer than 5 URLs, as this may result in inaccurate content strategy recommendations.

Problem

The AI content strategy analysis relies on sitemap URLs to understand the site's content. When:

• The sitemap is missing or inaccessible
• The sitemap contains very few URLs (< 5)

The generated recommendations may be incomplete or inaccurate. Users should be warned about this.

Proposed Solution

Display a warning message in both:

1. Admin UI (/admin/config/ai/content-strategy) - when viewing the report
2. CLI (drush acs:report and drush acs:sitemap) - in the JSON output

Warning conditions:

• sitemap_error: When sitemap cannot be fetched
• sitemap_warning: When sitemap has fewer than 5 URLs

CLI Note

Document that when running via Drush, users must pass -l <site-url> to ensure the correct sitemap URL is used:

drush acs:sitemap -l https://example.com

Acceptance Criteria

• Warning shown in UI when sitemap missing or < 5 URLs
• Warning included in CLI JSON output
• -l requirement documented in command help text