Add periodic health check email for abandoned plugins

[apermo]

Summary

• Adds a daily WP-Cron health check that scans all plugins for issues
• Sends a summary email when closed, stale (>2 years), or untested plugins are found
• Deduplicates via hash comparison — no repeat emails for unchanged issue sets
• Clears notification flag on plugin updates, activation/deactivation, and manual cache clear
• Email filterable via plugin_report_health_check_email

Closes #42

Architecture

Health check logic extracted into RT_Plugin_Report_Health_Check in includes/class-health-check.php — single responsibility, small testable methods:

• is_closed( $report ) — check if report indicates closed plugin
• is_stale( $report ) — check if not updated in 2+ years
• is_untested( $report, $wp_latest ) — check if not tested with current WP
• collect_warnings() — iterate all plugins, return categorized warnings
• build_email( $warnings ) — compose the email data array
• already_notified( $warnings ) — hash-based deduplication
• clear_notification_flag() — reset on plugin changes

Cron hook registered outside is_admin() so WP-Cron can fire it.

Test plan (local, no Playground — email requires real wp_mail)

• Activate plugin, verify cron event is scheduled (wp cron event list)
• Trigger manually: wp cron event run plugin_report_health_check
• Install a closed/stale plugin and verify email is sent
• Run again without changes — verify no duplicate email
• Update/remove a flagged plugin, run again — verify new email with updated set
• Deactivate plugin, verify cron event is cleared

[apermo]

@Zodiac1978 I haven't tested this yet, but it looks good to me, will you take over from here if it fits your vision?

[Zodiac1978]

I'm not sure how fast I can review this more deeply, but the described workflow looks fine to me.

[apermo]

Just take your time :)