feat(server): metrics schema + context with record/latest/prune

server/priv/repo/migrations/20260421202512_create_metrics.exs

@@ -0,0 +1,17 @@
+defmodule Server.Repo.Migrations.CreateMetrics do
+  use Ecto.Migration
+
+  def change do
+    create table(:metrics) do
+      add :host_id, references(:hosts, on_delete: :delete_all), null: false
+      add :collected_at, :utc_datetime_usec, null: false
+      add :interval_type, :string, null: false
+      add :payload, :string, null: false
+
+      timestamps(type: :utc_datetime_usec, updated_at: false)
+    end
+
+    create index(:metrics, [:host_id, :collected_at])
+    create index(:metrics, [:collected_at])
+  end
+end