feat: unified watch server under org-garden

org-garden/lib/org_garden/resolvers/doi.ex

@@ -0,0 +1,18 @@
+defmodule OrgGarden.Resolvers.DOI do
+  @moduledoc """
+  Last-resort citation resolver — always succeeds.
+
+  If the citation key looks like a DOI (starts with "10."), returns a
+  `https://doi.org/...` link. Otherwise returns the key itself as a
+  plain label with no URL.
+  """
+
+  @spec resolve(String.t()) :: {:ok, map()}
+  def resolve(key) do
+    if String.starts_with?(key, "10.") do
+      {:ok, %{label: key, url: "https://doi.org/#{key}"}}
+    else
+      {:ok, %{label: key, url: nil}}
+    end
+  end
+end