only enable gzip static file serving in prod

Avoids stale .gz files from mix assets.deploy shadowing freshly-built
dev assets. This was causing the admin to render with old DaisyUI dark
theme CSS even after the unified theme migration.

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

lib/berrypod_web/endpoint.ex

@@ -16,14 +16,12 @@ defmodule BerrypodWeb.Endpoint do
     longpoll: [connect_info: [session: @session_options]]
 
   # Serve at "/" the static files from "priv/static" directory.
-  # gzip is always enabled — Plug.Static serves .gz files when they exist
-  # (created by `mix phx.digest`), falls back to uncompressed otherwise.
-  # In prod, digested filenames change per deploy so immutable caching is safe.
-  # In dev, we omit the option to get the Plug.Static default ("public").
+  # gzip only in prod — avoids stale .gz files from mix assets.deploy
+  # shadowing freshly-built dev assets.
   plug Plug.Static,
     at: "/",
     from: :berrypod,
-    gzip: true,
+    gzip: Application.compile_env(:berrypod, :env) == :prod,
     only: BerrypodWeb.static_paths(),
     cache_control_for_etags:
       if(Application.compile_env(:berrypod, :env) == :prod,