feat(dashboard): merge top summary strip + Status widget into one Overview

Operator chose a single canonical summary. Repurpose the status_overview
widget into 'Overview' (host count + monitor up/down/pending + Alerts link;
key kept so existing dashboards upgrade in place) and remove the redundant
fixed top strip from the dashboard view. Drops _get_summary_stats and its
now-unused PingResult/DnsResult imports (rule 22).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/status/routes.py

@@ -1,8 +1,10 @@
 from __future__ import annotations
 from quart import Blueprint, current_app, render_template, request
+from sqlalchemy import func, select
 
 from steward.auth.middleware import require_role
 from steward.core.status import collect_status, sparkline_svg
+from steward.models.hosts import Host
 from steward.models.users import UserRole
 
 status_bp = Blueprint("status", __name__, url_prefix="/status")
@@ -40,12 +42,17 @@ async def rows():
 @status_bp.get("/widget")
 @require_role(UserRole.viewer)
 async def widget():
-    """HTMX dashboard widget — compact up/down/pending summary + problem list."""
+    """HTMX dashboard 'Overview' widget — the single at-a-glance summary that
+    replaced the old fixed top strip: host count + monitor up/down/pending +
+    problem list + an alerts link."""
     async with current_app.db_sessionmaker() as db:
         entries = await collect_status(db)
+        total_hosts = (await db.execute(
+            select(func.count()).select_from(Host))).scalar()
     up, down, pending = _summarize(entries)
     return await render_template(
         "status/widget.html",
         entries=entries, up=up, down=down, pending=pending,
+        total_hosts=total_hosts,
         widget_id=request.args.get("wid", "0"),
     )