feat: datasheet upload and auto-retrieve

- store datasheet PDFs on the server
- download PDF automatically when given a link

priv/repo/migrations/20250919205043_add_datasheet_filename_to_components.exs

@@ -0,0 +1,9 @@
+defmodule ComponentsElixir.Repo.Migrations.AddDatasheetFilenameToComponents do
+  use Ecto.Migration
+
+  def change do
+    alter table(:components) do
+      add :datasheet_filename, :string
+    end
+  end
+end