persist mockup variants on fly volume across deploys

Source mockup WebPs are copied from the release to /data/mockups/
on startup, and variants are generated there. This eliminates the
182-job storm on every deploy that was saturating the CPU and
causing SQLite locking. After the first successful run, subsequent
deploys find all variants intact.

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

lib/berrypod/images/variant_cache.ex

@@ -19,7 +19,13 @@ defmodule Berrypod.Images.VariantCache do
   alias Berrypod.Sync.ImageDownloadWorker
   import Ecto.Query
 
-  defp mockup_dir, do: Application.app_dir(:berrypod, "priv/static/mockups")
+  # Source mockups bundled in the release
+  defp release_mockup_dir, do: Application.app_dir(:berrypod, "priv/static/mockups")
+
+  # Where mockup variants live — persistent volume in prod, release dir in dev
+  defp mockup_dir do
+    Application.get_env(:berrypod, :mockup_dir) || release_mockup_dir()
+  end
 
   def start_link(opts) do
     GenServer.start_link(__MODULE__, opts, name: __MODULE__)
@@ -84,9 +90,25 @@ defmodule Berrypod.Images.VariantCache do
   end
 
   defp ensure_mockup_variants do
-    if File.dir?(mockup_dir()) do
+    output = mockup_dir()
+    release = release_mockup_dir()
+
+    # When using a persistent volume, copy source WebPs from the release
+    # so variants can be generated there (and survive deploys).
+    if output != release and File.dir?(release) do
+      File.mkdir_p!(output)
+
+      Path.wildcard(Path.join(release, "*.webp"))
+      |> Enum.reject(&is_variant?/1)
+      |> Enum.each(fn src ->
+        dest = Path.join(output, Path.basename(src))
+        unless File.exists?(dest), do: File.cp!(src, dest)
+      end)
+    end
+
+    if File.dir?(output) do
       sources =
-        Path.wildcard(Path.join(mockup_dir(), "*.webp"))
+        Path.wildcard(Path.join(output, "*.webp"))
         |> Enum.reject(&is_variant?/1)
 
       missing = Enum.reject(sources, &mockup_variants_exist?/1)