Bring the dashboard in line with the unified host IA + improved displays.
- New core "Hosts — Overview" widget (/hosts/overview/widget): one row per host
combining monitor status (ping dot + latency, uptime 24h) with the agent
glance (CPU / memory / disk root + stale flag), each row linking to the host
hub. Reads agent data from the generic PluginMetric table via a core-safe
_agent_overview_by_host helper (no host_agent import); freshness vs the
plugin's stale window. The granular Ping/DNS/Uptime/Agent widgets stay.
- Group the add-widget picker into Core monitors / Monitoring capabilities /
Integrations (a `group` field on every WIDGET_REGISTRY entry + section
headings in _edit_panels.html), matching the Settings → Plugins taxonomy.
- Fix the agent fleet widget rows to link to the host hub (/hosts/<id>) instead
of the old /plugins/host_agent/<id>/ page.
Scribe #903.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
