add image picker to page editor and fix thumbnail layout

Wire up image field in block settings with a modal picker that
browses the media library. Fix picker thumbnails collapsing to
14px by replacing overflow:hidden with overflow:clip on grid
items (hidden sets min-height:0 in grid context). Polish media
library mobile sheet with scrim overlay and tighter spacing.

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

lib/berrypod_web/page_renderer.ex

@@ -142,6 +142,14 @@ defmodule BerrypodWeb.PageRenderer do
           filter={@editor_picker_filter}
           event_prefix="editor_"
         />
+
+        <%!-- Image picker modal --%>
+        <.image_picker
+          :if={@editor_image_picker_block_id}
+          images={@editor_image_picker_images}
+          search={@editor_image_picker_search}
+          event_prefix="editor_"
+        />
       </aside>
 
       <%!-- Backdrop: tapping the page dismisses the sidebar --%>
@@ -1029,7 +1037,13 @@ defmodule BerrypodWeb.PageRenderer do
           if image.is_svg do
             "/image_cache/#{image.id}.webp"
           else
-            "/image_cache/#{image.id}-800.webp"
+            # Pick the largest variant that was actually generated
+            width =
+              image.source_width
+              |> Berrypod.Images.Optimizer.applicable_widths()
+              |> List.last()
+
+            "/image_cache/#{image.id}-#{width || 400}.webp"
           end
 
         {url, image.alt || image.filename}