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>

steward/migrations/versions/0032_retire_duplicate_widgets.py

@@ -0,0 +1,52 @@
+"""Merge duplicate dashboard widgets into the one that covers both (#5213)
+
+Revision ID: 0032_retire_duplicate_widgets
+Revises: 0031_ansible_run_origin
+Create Date: 2026-10-07
+
+Host Agent — Resources (host_resources) folds into Hosts — Overview
+(hosts_overview), and UniFi — Devices (unifi_devices) into UniFi — Overview
+(unifi_overview); widgets.RETIRED names the pairs. A dashboard that already
+shows the surviving widget loses the retired placement; any other keeps its
+cell, now showing the survivor. The old widget's own options don't apply to
+the new one, so they are cleared.
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "0032_retire_duplicate_widgets"
+down_revision: Union[str, None] = "0031_ansible_run_origin"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+# Frozen here rather than imported: a migration keeps meaning what it meant.
+_PAIRS = (("host_resources", "hosts_overview"), ("unifi_devices", "unifi_overview"))
+
+
+def upgrade() -> None:
+    for old, new in _PAIRS:
+        op.execute(sa.text("""
+            DELETE FROM dashboard_widgets d
+            WHERE d.widget_key = :old
+              AND EXISTS (SELECT 1 FROM dashboard_widgets k
+                          WHERE k.dashboard_id = d.dashboard_id AND k.widget_key = :new)
+        """).bindparams(old=old, new=new))
+        # Two placements of the old widget on one dashboard: keep the first.
+        op.execute(sa.text("""
+            DELETE FROM dashboard_widgets d
+            WHERE d.widget_key = :old
+              AND EXISTS (SELECT 1 FROM dashboard_widgets k
+                          WHERE k.dashboard_id = d.dashboard_id AND k.widget_key = :old
+                            AND k.id < d.id)
+        """).bindparams(old=old))
+        op.execute(sa.text("""
+            UPDATE dashboard_widgets SET widget_key = :new, config_json = NULL
+            WHERE widget_key = :old
+        """).bindparams(old=old, new=new))
+
+
+def downgrade() -> None:
+    # The merge is one-way: which survivor cells were once the retired widget
+    # isn't recorded, and the retired widgets no longer exist to render.
+    pass