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/src/assets/styles/utilities.less

@@ -15,15 +15,21 @@
 // ─────────────────────────────────────────────────────────────────────────
 
 // ── Design tokens ────────────────────────────────────────────────────
-// Legacy themeConfig.js + vue.config.js modifyVars. These are also fed to the
-// ant LESS build in vite.config.ts; declaring them here as custom properties
-// makes them reachable from plain CSS too (App.vue:65 reads --primary-color).
+// Legacy themeConfig.js + vue.config.js modifyVars. `--primary-color` is also
+// fed to ant itself via App.vue's <a-config-provider :theme> (ant-design-vue 4
+// replaced LESS modifyVars with CSS-in-JS design tokens); declaring it here as
+// a custom property keeps it reachable from plain CSS too (App.vue reads it).
 //
-// NOTE ant.less:5-7 declares `--primary: #41b883` / `--accent: #35495e` —
+// `--secondary-color` / `--third-color` were never real ant LESS variables
+// (confirmed dead in the old build — ant never consumed them), so they exist
+// only here for application code to use directly; they are not passed to
+// ConfigProvider.
+//
+// The old ant.less also declared `--primary: #41b883` / `--accent: #35495e` —
 // ant-design-pro boilerplate in Vue's own palette, inherited verbatim from
-// legacy. `--accent` drives @border-color-base, i.e. EVERY ant border. It is
-// left alone here (changing it is a visual decision, not a bug fix), but the
-// Henza tokens below are what application code should use.
+// legacy and used as `@border-color-base`. That file is deleted (ADV4 has no
+// LESS build to feed); nothing in the app should reference `--primary`/
+// `--accent` any more — use the Henza tokens below instead.
 :root {
   --primary-color: #1c2d56;
   --secondary-color: #836447;