Initial commit: homelab dashboard

Elixir + Phoenix dashboard displaying public and internal homelab
services. Internal services are shown only when the request originates
from the local network, detected server-side via conn.remote_ip with
Traefik trusted as a proxy (RemoteIp plug).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/homelab_dashboard_web/telemetry.ex

@@ -0,0 +1,70 @@
+defmodule HomelabDashboardWeb.Telemetry do
+  use Supervisor
+  import Telemetry.Metrics
+
+  def start_link(arg) do
+    Supervisor.start_link(__MODULE__, arg, name: __MODULE__)
+  end
+
+  @impl true
+  def init(_arg) do
+    children = [
+      # Telemetry poller will execute the given period measurements
+      # every 10_000ms. Learn more here: https://hexdocs.pm/telemetry_metrics
+      {:telemetry_poller, measurements: periodic_measurements(), period: 10_000}
+      # Add reporters as children of your supervision tree.
+      # {Telemetry.Metrics.ConsoleReporter, metrics: metrics()}
+    ]
+
+    Supervisor.init(children, strategy: :one_for_one)
+  end
+
+  def metrics do
+    [
+      # Phoenix Metrics
+      summary("phoenix.endpoint.start.system_time",
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.endpoint.stop.duration",
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.router_dispatch.start.system_time",
+        tags: [:route],
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.router_dispatch.exception.duration",
+        tags: [:route],
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.router_dispatch.stop.duration",
+        tags: [:route],
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.socket_connected.duration",
+        unit: {:native, :millisecond}
+      ),
+      sum("phoenix.socket_drain.count"),
+      summary("phoenix.channel_joined.duration",
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.channel_handled_in.duration",
+        tags: [:event],
+        unit: {:native, :millisecond}
+      ),
+
+      # VM Metrics
+      summary("vm.memory.total", unit: {:byte, :kilobyte}),
+      summary("vm.total_run_queue_lengths.total"),
+      summary("vm.total_run_queue_lengths.cpu"),
+      summary("vm.total_run_queue_lengths.io")
+    ]
+  end
+
+  defp periodic_measurements do
+    [
+      # A module, function and arguments to be invoked periodically.
+      # This function must call :telemetry.execute/3 and a metric must be added above.
+      # {HomelabDashboardWeb, :count_users, []}
+    ]
+  end
+end