feat(dashboard): a curated default layout, merged duplicate widgets, a labelled Overview (#5213)

- New installs start from widgets.RECOMMENDED, packed row by row for the
  enabled plugins; the edit drawer can reset a dashboard to it.
- Host Agent — Resources folds into Hosts — Overview (which gains load 1m),
  UniFi — Devices into UniFi — Overview; migration 0032 moves existing
  dashboards onto the survivors.
- The Overview labels what it counts (hosts, monitors up/down/pending,
  alerts firing) and lists firing alerts and down monitors with since-times.
- Uptime polls every 5 minutes (poll_seconds) instead of every cycle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plugins/host-agent-design.md

@@ -157,7 +157,6 @@ plugins/host_agent/
 │       └── host_agent_001_initial.py    # creates host_agent_registrations table
 ├── templates/
 │   ├── detail.html                      # per-host detail page
-│   ├── widget_table.html                # dashboard fleet table widget
 │   ├── widget_history.html              # dashboard history chart widget
 │   ├── settings_list.html               # plugin settings: list of registered hosts
 │   └── install.sh.j2                    # install script template (Jinja)
@@ -438,7 +437,7 @@ echo "Logs:          journalctl -u steward-agent -f"
 
 ### Dashboard widgets (`steward/core/widgets.py`)
 
-- **`host_resources`** — table widget. One row per monitored host: name, CPU %, mem %, disk % (worst mount), load 1m, "last seen Xs ago" with red/yellow/green coloring. Fleet glance.
+- The fleet glance (CPU, mem, disk /, load 1m, stale mark) is the core **Hosts — Overview** widget (`hosts_overview`); the old `host_resources` table was folded into it (#5213).
 - **`host_resource_history`** — chart widget for one host. CPU / mem / disk over a selectable time range (1h, 6h, 24h, 7d). Same pattern as every other history widget — Chart.js.
 
 ### Per-host detail page