remove Tailwind + DaisyUI theme + heroicons plugin, admin fully custom CSS (Phase 7)

replace Tailwind CLI with esbuild for admin CSS bundling. admin now uses
hand-written utility classes (admin/utilities.css), static heroicon CSS
generated by mix generate_admin_icons, plain CSS colour themes extracted
from DaisyUI plugin config, and minimal resets. rename app.css to admin.css
for clarity alongside shop.css. delete vendor/daisyui-theme.js and
vendor/heroicons.js. no Tailwind dependency remains in the project.

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

mix.exs

@@ -54,7 +54,6 @@ defmodule SimpleshopTheme.MixProject do
       {:lazy_html, ">= 0.1.0", only: :test},
       {:phoenix_live_dashboard, "~> 0.8.3"},
       {:esbuild, "~> 0.10", runtime: Mix.env() == :dev},
-      {:tailwind, "~> 0.3", runtime: Mix.env() == :dev},
       {:heroicons,
        github: "tailwindlabs/heroicons",
        tag: "v2.2.0",
@@ -95,17 +94,17 @@ defmodule SimpleshopTheme.MixProject do
       "ecto.setup": ["ecto.create", "ecto.migrate", "run priv/repo/seeds.exs"],
       "ecto.reset": ["ecto.drop", "ecto.setup"],
       test: ["ecto.create --quiet", "ecto.migrate --quiet", "test"],
-      "assets.setup": ["tailwind.install --if-missing", "esbuild.install --if-missing"],
+      "assets.setup": ["esbuild.install --if-missing"],
       "assets.build": [
         "compile",
-        "tailwind simpleshop_theme",
         "esbuild simpleshop_theme",
-        "esbuild simpleshop_theme_shop_css"
+        "esbuild simpleshop_theme_shop_css",
+        "esbuild simpleshop_theme_admin_css"
       ],
       "assets.deploy": [
-        "tailwind simpleshop_theme --minify",
         "esbuild simpleshop_theme --minify",
         "esbuild simpleshop_theme_shop_css --minify",
+        "esbuild simpleshop_theme_admin_css --minify",
         "phx.digest"
       ],
       precommit: ["compile --warning-as-errors", "deps.unlock --unused", "format", "test"],