separate editor FAB and panel for cleaner animation

Split the editor sheet into two distinct elements:
- .editor-fab: floating action button, always a pill in the corner
- .editor-panel: sliding panel that animates in/out independently

This enables proper CSS keyframe animations (slide-up/down on mobile,
slide-in/out on desktop) with a closing class for exit transitions.
Simplified the JS hook to only handle close behaviour.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/berrypod_web/live/shop/custom_page_test.exs

@@ -125,13 +125,13 @@ defmodule BerrypodWeb.Shop.CustomPageTest do
       {:ok, view, _html} = live(conn, "/editable")
 
       # Editor sheet should be visible for admins
-      assert has_element?(view, ".editor-sheet")
+      assert has_element?(view, ".editor-panel")
 
       # Click the edit button in the sheet to enter edit mode
-      view |> element(".editor-sheet-edit-btn") |> render_click()
+      view |> element(".editor-fab") |> render_click()
 
       # Now the editor sheet content should be visible (sheet state changes to open)
-      assert has_element?(view, ".editor-sheet-content")
+      assert has_element?(view, ".editor-panel-content")
     end
   end
 end