docs: add UI refinement to 20260114.1 release notes

Added button spacing standardization to improvements section of whats-new.json.
This documents the UI consistency work that standardized spacing, padding, and
icon sizes across Model/Prompt/Personality pickers and toolbar buttons.

Author: fewtarius

Resources/whats-new.json

@@ -20,6 +20,12 @@
       ],
       "bugfixes": [],
       "improvements": [
+        {
+          "id": "ui-button-spacing",
+          "icon": "ruler",
+          "title": "Refined UI Button Spacing and Consistency",
+          "description": "Standardized spacing, padding, and icon sizes across all UI controls. Model, Prompt, and Personality pickers now have identical padding (8px horizontal), button icons are consistently 20x20 points, and HStack spacing matches throughout the toolbar. This creates a more visually harmonious and polished interface."
+        },
         {
           "id": "split-model-support",
           "icon": "doc.on.doc",