Enrich native plugin list table with repository health data

[apermo]

Problem

Plugin health data (repository status, last update, tested-up-to version) currently only lives on a separate report page. Admins don't see this information where they actually manage plugins — the native Plugins list table.

Proposed changes

Add columns to the Plugins page

Hook into WordPress core's plugin list table via manage_plugins_columns and manage_plugins_custom_column to show:

• Repository — wp.org / closed / self-hosted / none
• Last Update — human-readable time diff with color coding
• Tested up to — WP version with color coding

Inline warnings

Use after_plugin_row_{$plugin_file} to show full-width warning rows beneath problematic plugins:

• Plugin closed on wp.org → red warning
• Not updated in >2 years → yellow warning
• Not tested with current WP major version → yellow warning

Data strategy

• If cached data exists (from report page visit) → show immediately
• If no cache → show "—" (don't trigger API calls on every plugin list page load)

Multisite

Needs verification of correct filter names for network admin plugin list.

Files

• rt-plugin-report.php — new hooks and rendering methods
• css/plugin-report.css — styles for new columns and warning rows
• README.txt / README.md — document new feature

[apermo]

Moved to Zodiac1978#85, draft PR at Zodiac1978#86.