feat(alt-text): add dashboard health widget

[srjaykikani]

Summary

• add a cached Alt text health dashboard widget for the alt-text plugin
• aggregate complete, missing, and partially localized alt-text coverage across all configured upload collections
• invalidate cached health results after create, update, and delete operations in configured upload collections
• expose the widget and health helper from the plugin server export and wire the example app import map/types

Testing

• pnpm lint in alt-text
• pnpm build in alt-text
• manually tested the dashboard in alt-text/dev with seeded media across media and images
• manually verified the dashboard counts updated after saving a media document with a single-locale alt text change

[jhb-dev]

Thanks for the work on this, Jay! I made a few adjustments on top — simplified the widget (fewer status tiers, cleaner layout), and made the unhealthy badge a clickable link that filters to the affected images by ID.

I also refactored the health check into a broader feature: in addition to the dashboard widget, the health data is now exposed via a REST endpoint (GET /api/alt-text-plugin/health) so that agents (MCP, CI, custom tooling) can consume it too. The whole feature can be opted out of via a single healthCheck: false config option, which disables the endpoint, cache revalidation hooks, and the widget.

This is part of a larger direction I want to take across all plugins — making them more agent-friendly by ensuring key data is accessible programmatically, not just through the admin UI.

[srjaykikani]

Followed up on your health-feature direction and pushed two commits to codex/issue-57-alt-text-health-widget:

• 6cc9ddc feat(alt-text): formalize health contract
• 0491a83 refactor(alt-text): simplify health widget flow

What changed relative to your comment:

• kept healthCheck as the single umbrella switch for endpoint + revalidation + widget
• kept the widget simple again, with the unhealthy badge still linking to the affected docs
• kept the REST surface as the programmatic source for agents / CI / tooling
• added a local machine-readable health contract in alt-text so the endpoint and widget can share one health computation without turning the widget back into the spec
• added structured error logging around the health route and cache revalidation
• fixed a regression in the cache wrapper that was causing the dashboard and /api/alt-text-plugin/health to throw Converting circular structure to JSON

Verification:

• pnpm test:health
• pnpm build
• live browser verification against alt-text/dev
• live endpoint check for /api/alt-text-plugin/health
• verified the unhealthy badge drilldown lands on the filtered collection view