admin-panel: upgrade to ant-design-vue 4.2.6

- Bump ant-design-vue 3.2.20 -> 4.2.6, @ant-design/icons-vue 6.1.0 -> 7.0.1.
- ADV4 removed LESS theming (modifyVars) for CSS-in-JS design tokens: drop
  the vite.config.ts modifyVars block and the antd.less import; move the
  three tokens ant actually consumed (primary/link/border-radius) to
  App.vue's <a-config-provider :theme>.
- Delete src/assets/styles/ant.less (426 lines of hand-written RTL flips):
  ADV4 renders RTL natively via CSS logical properties given direction="rtl",
  which App.vue already sets. Preserve only the small residue ADV4 doesn't
  cover natively (upload filename LTR, select dropdown z-index, tabs nav
  direction) in a new rtl-overrides.css.
- Clean up the stale --primary/--accent token comment in utilities.less now
  that ant.less is gone.
- Verified: pnpm build (vue-tsc -b && vite build) passes with zero errors;
  the codebase already used v-model:open everywhere (no ADV3 visible prop
  usage to migrate).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/admin-panel/vite.config.ts

@@ -21,14 +21,10 @@ export default defineConfig(({ mode }) => {
     css: {
       preprocessorOptions: {
         less: {
-          // Verbatim from legacy vue.config.js configureWebpack less-loader modifyVars.
-          modifyVars: {
-            'primary-color': '#1c2d56',
-            'secondary-color': '#836447',
-            'third-color': '#f5cb55',
-            'link-color': '#1DA57A',
-            'border-radius-base': '6px',
-          },
+          // ant-design-vue 4 dropped LESS theming (modifyVars) for CSS-in-JS design
+          // tokens; the equivalent primary/link/radius tokens now live in
+          // App.vue's <a-config-provider :theme>. This block only compiles the
+          // app's own farsi.less/utilities.less, which have no LESS variables.
           javascriptEnabled: true,
         },
       },