add admin media library with image management and block picker integration

- Schema: alt, caption, tags fields on images table with metadata changeset
- Context: list_images with filters, find_usages, used_image_ids, delete_with_cleanup
- Admin UI: /admin/media with grid view, upload, filters, detail panel, metadata editing
- Block editor: :image field type for image_text and content_body blocks
- Page renderer: image_id resolution with legacy URL fallback
- Mobile: bottom sheet detail panel with slide-up animation
- CSS: uses correct --t-* admin theme tokens, admin-badge colour variants

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

lib/berrypod_web/page_renderer.ex

@@ -249,12 +249,13 @@ defmodule BerrypodWeb.PageRenderer do
 
   defp render_block(%{block: %{"type" => "image_text"}} = assigns) do
     settings = assigns.block["settings"] || %{}
+    image_url = resolve_block_image_url(settings["image_id"], settings["image_url"])
 
     assigns =
       assigns
       |> assign(:section_title, settings["title"] || "")
       |> assign(:section_description, settings["description"] || "")
-      |> assign(:image_url, settings["image_url"] || "")
+      |> assign(:image_url, image_url)
       |> assign(:link_text, settings["link_text"])
       |> assign(:link_href, settings["link_href"])
 
@@ -560,11 +561,12 @@ defmodule BerrypodWeb.PageRenderer do
   defp render_block(%{block: %{"type" => "content_body"}} = assigns) do
     settings = assigns.block["settings"] || %{}
     content = settings["content"] || ""
+    {image_src, image_alt} = resolve_content_image(settings)
 
     assigns =
       assigns
-      |> assign(:image_src, settings["image_src"])
-      |> assign(:image_alt, settings["image_alt"] || "")
+      |> assign(:image_src, image_src)
+      |> assign(:image_alt, image_alt)
       |> assign(:content, content)
 
     ~H"""
@@ -998,6 +1000,42 @@ defmodule BerrypodWeb.PageRenderer do
   defp collection_path(slug, "featured"), do: ~p"/collections/#{slug}"
   defp collection_path(slug, sort), do: ~p"/collections/#{slug}?sort=#{sort}"
 
+  # Resolves an image_id to a URL, falling back to a legacy URL string
+  defp resolve_block_image_url(image_id, fallback_url) do
+    case resolve_image(image_id) do
+      {url, _alt} -> url
+      nil -> fallback_url || ""
+    end
+  end
+
+  # Resolves image_id for content_body blocks, returning {src, alt}
+  defp resolve_content_image(settings) do
+    case resolve_image(settings["image_id"]) do
+      {src, alt} -> {src, alt}
+      nil -> {settings["image_src"], settings["image_alt"] || ""}
+    end
+  end
+
+  defp resolve_image(nil), do: nil
+  defp resolve_image(""), do: nil
+
+  defp resolve_image(image_id) do
+    case Berrypod.Media.get_image(image_id) do
+      nil ->
+        nil
+
+      image ->
+        url =
+          if image.is_svg do
+            "/image_cache/#{image.id}.webp"
+          else
+            "/image_cache/#{image.id}-800.webp"
+          end
+
+        {url, image.alt || image.filename}
+    end
+  end
+
   def format_order_status("unfulfilled"), do: "Being prepared"
   def format_order_status("submitted"), do: "Sent to printer"
   def format_order_status("processing"), do: "In production"