add undo/redo to page editors with keyboard shortcuts

History stacks (@history/@future) on both admin editor and live sidebar,
capped at 50 entries. All mutations routed through apply_mutation for
consistent history tracking. EditorKeyboard JS hook combines DirtyGuard
with Ctrl+Z/Ctrl+Shift+Z. Settings panel fade-in animation. 10 new tests.

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

lib/berrypod_web/page_editor_hook.ex

@@ -27,6 +27,8 @@ defmodule BerrypodWeb.PageEditorHook do
       |> assign(:editing, false)
       |> assign(:editing_blocks, nil)
       |> assign(:editor_dirty, false)
+      |> assign(:editor_history, [])
+      |> assign(:editor_future, [])
       |> assign(:editor_expanded, MapSet.new())
       |> assign(:editor_show_picker, false)
       |> assign(:editor_picker_filter, "")
@@ -141,11 +143,8 @@ defmodule BerrypodWeb.PageEditorHook do
       {:ok, new_blocks, message} ->
         socket =
           socket
-          |> assign(:editing_blocks, new_blocks)
-          |> assign(:editor_dirty, true)
+          |> apply_mutation(new_blocks, message, :content)
           |> assign(:editor_show_picker, false)
-          |> assign(:editor_live_region_message, message)
-          |> reload_block_data(new_blocks)
 
         {:halt, socket}
 
@@ -160,13 +159,7 @@ defmodule BerrypodWeb.PageEditorHook do
 
     case BlockEditor.update_settings(socket.assigns.editing_blocks, block_id, new_settings) do
       {:ok, new_blocks} ->
-        socket =
-          socket
-          |> assign(:editing_blocks, new_blocks)
-          |> assign(:editor_dirty, true)
-          |> reload_block_data(new_blocks)
-
-        {:halt, socket}
+        {:halt, apply_mutation(socket, new_blocks, "Settings updated", :content)}
 
       :noop ->
         {:halt, socket}
@@ -304,11 +297,9 @@ defmodule BerrypodWeb.PageEditorHook do
       {:ok, new_blocks} ->
         socket =
           socket
-          |> assign(:editing_blocks, new_blocks)
-          |> assign(:editor_dirty, true)
+          |> apply_mutation(new_blocks, "Image selected", :content)
           |> assign(:editor_image_picker_block_id, nil)
           |> assign(:editor_image_picker_field_key, nil)
-          |> reload_block_data(new_blocks)
 
         {:halt, socket}
 
@@ -326,15 +317,53 @@ defmodule BerrypodWeb.PageEditorHook do
            field_key => ""
          }) do
       {:ok, new_blocks} ->
+        {:halt, apply_mutation(socket, new_blocks, "Image cleared", :content)}
+
+      :noop ->
+        {:halt, socket}
+    end
+  end
+
+  # ── Undo / redo ──────────────────────────────────────────────────
+
+  defp handle_editor_action("undo", _params, socket) do
+    case socket.assigns.editor_history do
+      [prev | rest] ->
+        future = [socket.assigns.editing_blocks | socket.assigns.editor_future]
+
         socket =
           socket
-          |> assign(:editing_blocks, new_blocks)
+          |> assign(:editing_blocks, prev)
+          |> assign(:editor_history, rest)
+          |> assign(:editor_future, future)
           |> assign(:editor_dirty, true)
-          |> reload_block_data(new_blocks)
+          |> assign(:editor_live_region_message, "Undone")
+          |> reload_block_data(prev)
 
         {:halt, socket}
 
-      :noop ->
+      [] ->
+        {:halt, socket}
+    end
+  end
+
+  defp handle_editor_action("redo", _params, socket) do
+    case socket.assigns.editor_future do
+      [next | rest] ->
+        history = [socket.assigns.editing_blocks | socket.assigns.editor_history]
+
+        socket =
+          socket
+          |> assign(:editing_blocks, next)
+          |> assign(:editor_history, history)
+          |> assign(:editor_future, rest)
+          |> assign(:editor_dirty, true)
+          |> assign(:editor_live_region_message, "Redone")
+          |> reload_block_data(next)
+
+        {:halt, socket}
+
+      [] ->
         {:halt, socket}
     end
   end
@@ -353,6 +382,8 @@ defmodule BerrypodWeb.PageEditorHook do
           |> assign(:page, updated_page)
           |> assign(:editing_blocks, updated_page.blocks)
           |> assign(:editor_dirty, false)
+          |> assign(:editor_history, [])
+          |> assign(:editor_future, [])
           |> put_flash(:info, "Page saved")
 
         {:halt, socket}
@@ -372,6 +403,8 @@ defmodule BerrypodWeb.PageEditorHook do
       |> assign(:page, page)
       |> assign(:editing_blocks, page.blocks)
       |> assign(:editor_dirty, false)
+      |> assign(:editor_history, [])
+      |> assign(:editor_future, [])
       |> reload_block_data(page.blocks)
       |> put_flash(:info, "Page reset to defaults")
 
@@ -396,6 +429,8 @@ defmodule BerrypodWeb.PageEditorHook do
     |> assign(:editing, true)
     |> assign(:editing_blocks, page.blocks)
     |> assign(:editor_dirty, false)
+    |> assign(:editor_history, [])
+    |> assign(:editor_future, [])
     |> assign(:editor_expanded, MapSet.new())
     |> assign(:editor_show_picker, false)
     |> assign(:editor_picker_filter, "")
@@ -413,6 +448,8 @@ defmodule BerrypodWeb.PageEditorHook do
     |> assign(:editing, false)
     |> assign(:editing_blocks, nil)
     |> assign(:editor_dirty, false)
+    |> assign(:editor_history, [])
+    |> assign(:editor_future, [])
     |> assign(:editor_expanded, MapSet.new())
     |> assign(:editor_show_picker, false)
     |> assign(:editor_picker_filter, "")
@@ -426,9 +463,14 @@ defmodule BerrypodWeb.PageEditorHook do
   end
 
   defp apply_mutation(socket, new_blocks, message, type) do
+    history =
+      [socket.assigns.editing_blocks | socket.assigns.editor_history] |> Enum.take(50)
+
     socket =
       socket
       |> assign(:editing_blocks, new_blocks)
+      |> assign(:editor_history, history)
+      |> assign(:editor_future, [])
       |> assign(:editor_dirty, true)
       |> assign(:editor_live_region_message, message)