implement unified on-site editor phases 1-2

Add theme editing to the existing PageEditorHook, enabling on-site
theme customisation alongside page editing. The editor panel now has
three tabs (Page, Theme, Settings) and can be collapsed while
keeping editing state intact.

- Add theme editing state and event handlers to PageEditorHook
- Add 3-tab UI with tab switching logic
- Add transparent overlay for click-outside dismiss
- Add mobile drag-to-resize with height persistence
- Fix animation replay on drag release (has-dragged class)
- Preserve panel height across LiveView re-renders
- Default to Page tab on editable pages, Theme otherwise
- Show unsaved changes indicator on FAB when panel collapsed
- Fix handle_event grouping warning in admin theme

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

lib/berrypod_web/live/admin/theme/index.ex

@@ -326,10 +326,6 @@ defmodule BerrypodWeb.Admin.Theme.Index do
     end
   end
 
-  defp has_valid_logo?(socket) do
-    socket.assigns.theme_settings.show_logo && socket.assigns.logo_image != nil
-  end
-
   @impl true
   def handle_event("save_theme", _params, socket) do
     socket = put_flash(socket, :info, "Theme saved successfully")
@@ -452,6 +448,10 @@ defmodule BerrypodWeb.Admin.Theme.Index do
     {:noreply, socket}
   end
 
+  defp has_valid_logo?(socket) do
+    socket.assigns.theme_settings.show_logo && socket.assigns.logo_image != nil
+  end
+
   def error_to_string(:too_large), do: "File is too large"
   def error_to_string(:too_many_files), do: "Too many files"
   def error_to_string(:not_accepted), do: "File type not accepted"

lib/berrypod_web/live/admin/theme/index.html.heex

@@ -330,8 +330,7 @@
         <div class="theme-subfield">
           <form phx-change="update_setting" phx-value-field="favicon_short_name">
             <label class="theme-slider-label theme-block-label">
-              Short name
-              <span class="admin-text-tertiary">— appears under home screen icon</span>
+              Short name <span class="admin-text-tertiary">— appears under home screen icon</span>
             </label>
             <input
               type="text"
@@ -441,7 +440,7 @@
                 </div>
               </div>
             <% end %>
-
+            
 <!-- Header Image Controls -->
             <div class="admin-stack admin-stack-md theme-subfield">
               <form phx-change="update_setting" phx-value-field="header_zoom">
@@ -521,7 +520,7 @@
           <% end %>
         </div>
       <% end %>
-
+      
 <!-- Presets Section -->
       <div class="theme-section">
         <label class="theme-section-label">Start with a preset</label>