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/router.ex

@@ -105,6 +105,18 @@ defmodule BerrypodWeb.Router do
     get "/sitemap.xml", SeoController, :sitemap
   end
 
+  # Favicon & PWA manifest — served from DB, minimal pipeline
+  scope "/", BerrypodWeb do
+    pipe_through [:seo]
+
+    get "/favicon.svg", FaviconController, :favicon_svg
+    get "/favicon-32x32.png", FaviconController, :favicon_32
+    get "/apple-touch-icon.png", FaviconController, :apple_touch_icon
+    get "/icon-192.png", FaviconController, :icon_192
+    get "/icon-512.png", FaviconController, :icon_512
+    get "/site.webmanifest", FaviconController, :webmanifest
+  end
+
   # Cart API (session persistence for LiveView)
   scope "/api", BerrypodWeb do
     pipe_through [:browser]