add favicon and site icon generation from uploaded images

Upload a source image (PNG, JPEG, or SVG) and get a complete favicon
setup: PNG variants at 32, 180, 192, 512px served from DB via
FaviconController with ETag caching, SVG favicon for vector sources,
dynamic site.webmanifest, and theme-color meta tag. Theme editor gains
a site icon section with "use logo as icon" toggle, dedicated icon
upload, short name, and background colour picker.

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

lib/berrypod_web/controllers/favicon_controller.ex

@@ -0,0 +1,104 @@
+defmodule BerrypodWeb.FaviconController do
+  use BerrypodWeb, :controller
+
+  alias Berrypod.Media
+  alias Berrypod.Settings
+
+  @one_day 86_400
+
+  def favicon_svg(conn, _params) do
+    case Media.get_favicon_variants() do
+      %{svg: svg} when is_binary(svg) ->
+        conn
+        |> maybe_not_modified("svg")
+        |> serve("image/svg+xml", svg)
+
+      _ ->
+        send_resp(conn, 404, "")
+    end
+  end
+
+  def favicon_32(conn, _params), do: serve_variant(conn, :png_32)
+  def apple_touch_icon(conn, _params), do: serve_variant(conn, :png_180)
+  def icon_192(conn, _params), do: serve_variant(conn, :png_192)
+  def icon_512(conn, _params), do: serve_variant(conn, :png_512)
+
+  def webmanifest(conn, _params) do
+    settings = Settings.get_theme_settings()
+
+    short_name =
+      case settings.favicon_short_name do
+        name when is_binary(name) and name != "" -> name
+        _ -> String.slice(settings.site_name, 0, 12)
+      end
+
+    manifest = %{
+      name: settings.site_name,
+      short_name: short_name,
+      theme_color: settings.accent_color || "#000000",
+      background_color: settings.icon_background_color || "#ffffff",
+      display: "minimal-ui",
+      start_url: "/",
+      icons: [
+        %{src: "/icon-192.png", sizes: "192x192", type: "image/png"},
+        %{src: "/icon-512.png", sizes: "512x512", type: "image/png", purpose: "maskable"}
+      ]
+    }
+
+    conn
+    |> put_resp_content_type("application/manifest+json")
+    |> put_resp_header("cache-control", "public, max-age=#{@one_day}")
+    |> json(manifest)
+  end
+
+  defp serve_variant(conn, field) do
+    case Media.get_favicon_variants() do
+      nil ->
+        send_resp(conn, 404, "")
+
+      variants ->
+        case Map.get(variants, field) do
+          data when is_binary(data) ->
+            conn
+            |> maybe_not_modified(variants)
+            |> serve("image/png", data)
+
+          _ ->
+            send_resp(conn, 404, "")
+        end
+    end
+  end
+
+  defp maybe_not_modified(%{halted: true} = conn, _), do: conn
+
+  defp maybe_not_modified(conn, variants) do
+    etag = build_etag(variants)
+
+    case get_req_header(conn, "if-none-match") do
+      [^etag] ->
+        conn
+        |> put_resp_header("cache-control", "public, max-age=#{@one_day}")
+        |> put_resp_header("etag", etag)
+        |> send_resp(304, "")
+        |> halt()
+
+      _ ->
+        conn
+        |> put_resp_header("cache-control", "public, max-age=#{@one_day}")
+        |> put_resp_header("etag", etag)
+    end
+  end
+
+  defp serve(%{halted: true} = conn, _content_type, _data), do: conn
+
+  defp serve(conn, content_type, data) do
+    conn
+    |> put_resp_content_type(content_type)
+    |> send_resp(200, data)
+  end
+
+  defp build_etag(%{generated_at: %DateTime{} = dt}),
+    do: ~s("fav-#{DateTime.to_unix(dt)}")
+
+  defp build_etag(_), do: ~s("fav-0")
+end