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/components/block_editor_components.ex

@@ -206,6 +206,53 @@ defmodule BerrypodWeb.BlockEditorComponents do
     """
   end
 
+  def block_field(%{field: %{type: :image}} = assigns) do
+    image_id = assigns.value
+    image = if is_binary(image_id) && image_id != "", do: Berrypod.Media.get_image(image_id)
+    assigns = assign(assigns, :image, image)
+
+    ~H"""
+    <div class="admin-fieldset">
+      <span class="admin-label">{@field.label}</span>
+      <div class="image-field">
+        <%= if @image do %>
+          <div class="image-field-preview">
+            <%= if @image.is_svg do %>
+              <div class="image-field-svg">
+                <.icon name="hero-code-bracket" class="size-6" />
+              </div>
+            <% else %>
+              <img
+                src={"/image_cache/#{@image.id}-thumb.jpg"}
+                alt={@image.alt || @image.filename}
+                class="image-field-thumb"
+              />
+            <% end %>
+            <div class="image-field-info">
+              <span class="image-field-filename">{@image.filename}</span>
+              <span :if={@image.alt} class="image-field-alt">{@image.alt}</span>
+            </div>
+          </div>
+        <% else %>
+          <div class="image-field-empty">
+            <.icon name="hero-photo" class="size-6" />
+            <span>No image selected</span>
+          </div>
+        <% end %>
+        <input
+          type="text"
+          name={"block_settings[#{@field.key}]"}
+          id={"block-#{@block_id}-#{@field.key}"}
+          value={if(@image, do: @image.id, else: "")}
+          placeholder="Paste image ID from media library"
+          class="admin-input admin-input-sm"
+          phx-debounce="blur"
+        />
+      </div>
+    </div>
+    """
+  end
+
   def block_field(%{field: %{type: :repeater}} = assigns) do
     items = if is_list(assigns.value), do: assigns.value, else: []
     item_count = length(items)

lib/berrypod_web/components/layouts/admin.html.heex

@@ -102,6 +102,14 @@
               <.icon name="hero-document" class="size-5" /> Pages
             </.link>
           </li>
+          <li>
+            <.link
+              navigate={~p"/admin/media"}
+              class={admin_nav_active?(@current_path, "/admin/media")}
+            >
+              <.icon name="hero-photo" class="size-5" /> Media
+            </.link>
+          </li>
           <li>
             <.link
               href={~p"/admin/theme"}