refactor(ui): minimalistic utilitarian redesign across all views

New design language:
  - dark background, system sans for UI, monospace for data
  - single green accent, amber/red for warn/critical
  - square-bordered panels + tables, no rounded cards or shadows
  - status conveyed via left-border on overview cards + badges

Changes:
  - new app.css defines CSS vars + component classes (.panel, .tbl,
    .card, .btn, .input, .badge with [data-status=*])
  - new ServerWeb.DashboardNav function component for a shared top nav
    with active-link highlighting; replaces per-view navigation clutter
  - strip the Phoenix welcome scaffold (logo, version badge, twitter/GH
    links) from layouts/app.html.heex; leaves only flash + content
  - root.html.heex title suffix switched to 'Proxmox Monitor', body
    loses the Tailwind-white background
  - rewrite render/1 in all four LiveViews + login template to use the
    new classes; admin form now uses <.form for={@form}> and properly
    clears on success
  - login page redesigned to a single tight panel matching the rest

All 58 tests still pass; 'mix compile --warnings-as-errors' is clean.

server/lib/server_web/live/overview_live.ex

@@ -6,7 +6,7 @@ defmodule ServerWeb.OverviewLive do
   @impl true
   def mount(_params, _session, socket) do
     if connected?(socket), do: Phoenix.PubSub.subscribe(Server.PubSub, "metrics")
-    {:ok, assign(socket, :hosts, load_hosts())}
+    {:ok, assign(socket, hosts: load_hosts(), page_title: "Overview")}
   end
 
   @impl true
@@ -25,70 +25,59 @@ defmodule ServerWeb.OverviewLive do
   @impl true
   def render(assigns) do
     ~H"""
-    <div class="p-6 max-w-6xl mx-auto space-y-6">
-      <header class="flex justify-between items-center">
-        <div class="space-x-4">
-          <h1 class="text-2xl font-bold inline">Proxmox Monitor</h1>
-          <.link navigate={~p"/vms"} class="text-sm text-zinc-600 hover:text-zinc-900">VMs</.link>
-          <.link navigate={~p"/admin/hosts"} class="text-sm text-zinc-600 hover:text-zinc-900">
-            Admin
-          </.link>
-        </div>
-        <.link href={~p"/logout"} method="delete" class="text-sm text-zinc-500">Sign out</.link>
-      </header>
+    <ServerWeb.DashboardNav.nav active={:overview} />
 
-      <div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
-        <div
-          :for={entry <- @hosts}
-          data-role="host-card"
-          data-status={Atom.to_string(entry.status)}
-          class={"p-4 rounded-lg border-l-4 bg-white shadow-sm " <> border_class(entry.status)}
-        >
-          <.link navigate={~p"/hosts/#{entry.host.name}"} class="block space-y-2">
-            <div class="flex justify-between items-baseline">
-              <span class="font-semibold text-zinc-900">{entry.host.name}</span>
-              <span class={"text-xs uppercase tracking-wide " <> text_class(entry.status)}>
-                {entry.status}
-              </span>
-            </div>
-            <div class="text-xs text-zinc-500">
-              Last seen: {last_seen(entry.host.last_seen_at)}
-            </div>
-            <div :if={entry.sample} class="text-sm text-zinc-700 space-y-1">
-              <div>Load: {format_load(entry.sample.payload)}</div>
-              <div>RAM used: {format_mem(entry.sample.payload)}</div>
-              <div>Pools: {pool_summary(entry.sample.payload)}</div>
-              <div>VMs: {vm_count(entry.sample.payload)}</div>
-            </div>
-            <div :if={is_nil(entry.sample)} class="text-sm text-zinc-400 italic">
-              No samples yet
-            </div>
-          </.link>
+    <div class="page">
+      <div class="pagehead">
+        <h1>Hosts</h1>
+        <span class="sub">{summary_line(@hosts)}</span>
+      </div>
+
+      <div :if={@hosts == []} class="panel">
+        <div class="empty">
+          No hosts registered. Add one at
+          <.link navigate={~p"/admin/hosts"}>/admin/hosts</.link>.
         </div>
       </div>
 
-      <p :if={@hosts == []} class="text-zinc-500">
-        No hosts registered yet. Add one via <code>/admin/hosts</code>.
-      </p>
+      <div class="cards">
+        <.link :for={entry <- @hosts} navigate={~p"/hosts/#{entry.host.name}"} class="card"
+              data-status={Atom.to_string(entry.status)} data-role="host-card">
+          <div class="row">
+            <span class="name">{entry.host.name}</span>
+            <span class="right badge" data-status={Atom.to_string(entry.status)}>
+              {entry.status}
+            </span>
+          </div>
+          <div class="seen">last seen {last_seen(entry.host.last_seen_at)}</div>
+          <%= if entry.sample do %>
+            <div class="stat"><span class="k">load</span><span class="v">{load(entry.sample.payload)}</span></div>
+            <div class="stat"><span class="k">ram</span><span class="v">{mem(entry.sample.payload)}</span></div>
+            <div class="stat"><span class="k">pools</span><span class="v">{pool_summary(entry.sample.payload)}</span></div>
+            <div class="stat"><span class="k">vms</span><span class="v">{vm_count(entry.sample.payload)}</span></div>
+          <% else %>
+            <div class="dim">no samples yet</div>
+          <% end %>
+        </.link>
+      </div>
     </div>
     """
   end
 
-  defp border_class(:ok), do: "border-green-500"
-  defp border_class(:warning), do: "border-yellow-500"
-  defp border_class(:critical), do: "border-red-500"
-  defp border_class(:offline), do: "border-zinc-400"
-
-  defp text_class(:ok), do: "text-green-600"
-  defp text_class(:warning), do: "text-yellow-600"
-  defp text_class(:critical), do: "text-red-600"
-  defp text_class(:offline), do: "text-zinc-500"
+  defp summary_line([]), do: "0 hosts"
+  defp summary_line(hosts) do
+    n = length(hosts)
+    by = Enum.frequencies_by(hosts, & &1.status)
+    parts =
+      [:ok, :warning, :critical, :offline]
+      |> Enum.filter(&Map.has_key?(by, &1))
+      |> Enum.map(fn s -> "#{by[s]} #{s}" end)
+    "#{n} host#{if n == 1, do: "", else: "s"} · " <> Enum.join(parts, " · ")
+  end
 
   defp last_seen(nil), do: "never"
-
   defp last_seen(%DateTime{} = dt) do
     secs = DateTime.diff(DateTime.utc_now(), dt, :second)
-
     cond do
       secs < 60 -> "#{secs}s ago"
       secs < 3600 -> "#{div(secs, 60)}m ago"
@@ -96,23 +85,20 @@ defmodule ServerWeb.OverviewLive do
     end
   end
 
-  defp format_load(payload) do
+  defp load(payload) do
     case get_in(payload, ["host", "load1"]) do
       nil -> "—"
       l -> :io_lib.format("~.2f", [l]) |> to_string()
     end
   end
 
-  defp format_mem(payload) do
+  defp mem(payload) do
     used = get_in(payload, ["host", "mem_used_bytes"])
     total = get_in(payload, ["host", "mem_total_bytes"])
-
     case {used, total} do
       {u, t} when is_integer(u) and is_integer(t) and t > 0 ->
         "#{Float.round(u / t * 100, 1)}%"
-
-      _ ->
-        "—"
+      _ -> "—"
     end
   end
 
@@ -120,11 +106,11 @@ defmodule ServerWeb.OverviewLive do
     pools = get_in(payload, ["zfs_pools", "pools"]) || []
     total = length(pools)
     bad = Enum.count(pools, &(&1["health"] != "ONLINE"))
-    if total == 0, do: "—", else: "#{total - bad}/#{total} ok"
+    if total == 0, do: "—", else: "#{total - bad}/#{total}"
   end
 
   defp vm_count(payload) do
     vms = get_in(payload, ["vms_runtime", "vms"]) || []
-    length(vms)
+    length(vms) |> to_string()
   end
 end