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>

tests/test_route_access.py

@@ -52,7 +52,7 @@ def test_every_route_says_who_may_reach_it():
 
 def test_the_scan_sees_routes():
     names = {n.name for _, text in _sources() for n, _ in route_views(text)}
-    assert {"login", "health", "ingest", "widget_table", "public_share"} <= names
+    assert {"login", "health", "ingest", "widget_history", "public_share"} <= names
 
 
 @pytest.mark.asyncio