feat(hosts): a host's health tiles span the card and the gaps match; Add host is a dialog on the list (#5290, #5291)

#5290 "Host page: the health tiles span the card's width; even spacing above Ansible":
the four tiles take equal quarters (halves on a phone) and their sparklines stretch
across them; the Monitors + Agent row drops the Agent card's own margin, so the gap
above Ansible is 1rem like every other.

#5291 "Add host opens as a dialog over the Hosts list": a native <dialog> on /hosts/,
opened by Add host or /hosts/?add=1. A name clash re-renders the list with it open,
the error and what was typed. GET /hosts/new is gone; hosts/form.html is Edit only.

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

steward/hosts/routes.py

@@ -41,6 +41,13 @@ async def overview_widget():
 @hosts_bp.get("/")
 @require_role(UserRole.viewer)
 async def list_hosts():
+    # ?add=1 opens the Add host dialog on load (#5291).
+    return await _list_page(add={} if request.args.get("add") else None)
+
+
+async def _list_page(add: dict | None = None):
+    """The Hosts list. `add` opens the Add host dialog: {} for an empty form,
+    or {"values": form, "error": msg} when a submit comes back."""
     async with current_app.db_sessionmaker() as db:
         result = await db.execute(select(Host).order_by(Host.name))
         hosts = result.scalars().all()
@@ -57,6 +64,7 @@ async def list_hosts():
         host_status=host_status,
         uptime=uptime,
         agent=agent,
+        add=add,
     )
 
 
@@ -93,12 +101,6 @@ async def host_detail(host_id: str):
     )
 
 
-@hosts_bp.get("/new")
-@require_role(UserRole.operator)
-async def new_host():
-    return await render_template("hosts/form.html", host=None)
-
-
 @hosts_bp.post("/")
 @require_role(UserRole.operator)
 async def create_host():
@@ -112,8 +114,7 @@ async def create_host():
             try:
                 await host_svc.check_name_free(db, host.name)
             except ValueError as exc:
-                return await render_template("hosts/form.html", host=None, values=form,
-                                             error=str(exc)), 400
+                return await _list_page(add={"values": form, "error": str(exc)}), 400
             db.add(host)
     await log_audit(current_app, session.get("user_id"), session.get("username", ""),
                     "host.created", entity_type="host", entity_id=host.name,