complete admin CSS refactor: delete utilities.css, add layout primitives

- Delete utilities.css (701 lines / 24 KB of Tailwind utility clones)
- Add layout.css with admin-stack, admin-row, admin-cluster, admin-grid
  primitives and gap variants (sm, md, lg, xl)
- Add transitions.css import and layout.css import to admin.css entry point
- Replace all Tailwind utility classes across 26 admin templates with
  semantic admin-*/theme-*/page-specific CSS classes
- Replace all non-dynamic inline styles with semantic classes
- Add ~100 new semantic classes to components.css (analytics, dashboard,
  order detail, settings, theme editor, generic utilities)
- Fix stray text-error → admin-text-error in media.ex
- Add missing .truncate definition to admin CSS
- Only remaining inline styles are dynamic data values (progress bars,
  chart dimensions) and one JS.toggle target

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

lib/berrypod_web/live/admin/pages/custom_form.ex

@@ -118,10 +118,7 @@ defmodule BerrypodWeb.Admin.Pages.CustomForm do
   @impl true
   def render(assigns) do
     ~H"""
-    <.link
-      navigate={~p"/admin/pages"}
-      class="text-sm font-normal text-base-content/60 hover:underline"
-    >
+    <.link navigate={~p"/admin/pages"} class="admin-back-link">
       &larr; Pages
     </.link>
 
@@ -153,8 +150,7 @@ defmodule BerrypodWeb.Admin.Pages.CustomForm do
       id="custom-page-form"
       phx-change="validate"
       phx-submit="save"
-      class="mt-6 space-y-6"
-      style="max-width: 32rem;"
+      class="admin-form-stack admin-section"
     >
       <.input field={@form[:title]} label="Title" />
       <.input field={@form[:slug]} label="URL slug" />
@@ -167,12 +163,15 @@ defmodule BerrypodWeb.Admin.Pages.CustomForm do
       <.input field={@form[:published]} type="checkbox" label="Published" />
       <.input field={@form[:show_in_nav]} type="checkbox" label="Show in navigation" />
 
-      <div :if={@form[:show_in_nav].value == true} class="space-y-4 pl-6">
+      <div
+        :if={@form[:show_in_nav].value == true}
+        class="admin-form-sub"
+      >
         <.input field={@form[:nav_label]} label="Nav label" />
         <.input field={@form[:nav_position]} type="number" label="Nav position" />
       </div>
 
-      <div class="flex gap-3">
+      <div class="admin-row admin-row-lg">
         <.button type="submit" phx-disable-with="Saving...">
           {if @live_action == :new, do: "Create page", else: "Save settings"}
         </.button>