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/package.json

@@ -11,10 +11,10 @@
     "lint": "eslint \"src/**/*.{ts,vue}\""
   },
   "dependencies": {
-    "@ant-design/icons-vue": "^6.1.0",
+    "@ant-design/icons-vue": "^7.0.1",
     "@gold-bank/shared-types": "workspace:*",
     "@vueuse/core": "^9.13.0",
-    "ant-design-vue": "^3.2.20",
+    "ant-design-vue": "^4.2.6",
     "axios": "^1.7.7",
     "lodash": "^4.17.21",
     "moment-jalaali": "^0.10.0",