fix(dashboard): Minor cleanup and improve text legibility (#7045)

**What**
- Cleans up some artifacts from the V1 -> V2 migrations.
- Removes the MedusaProvider from the root in favor of a plain QueryClient.
- Applies font styles to make the text in admin resemble designs in Figma more closely.

packages/admin-next/dashboard/src/index.css

@@ -28,7 +28,8 @@
   }
 
   :root {
-    @apply bg-ui-bg-subtle text-ui-fg-base;
+    @apply bg-ui-bg-subtle text-ui-fg-base antialiased;
+    text-rendering: optimizeLegibility;
   }
 }