feat(ui): add DateRangePicker component

Adds a new DateRangePicker component to @backstage/ui built on React Aria,
featuring a custom field group with two DateInput fields and a calendar
trigger, a RangeCalendar popover with proper range selection visuals
(solid circles for start/end, transparent solid fill for in-range cells
with row-boundary rounding), and full BUI token usage including bg
consumer auto-increment. Includes Storybook stories and a docs-ui page.

Signed-off-by: Charles de Dreuille <charles.dedreuille@gmail.com>
Made-with: Cursor

packages/ui/package.json

@@ -47,6 +47,7 @@
   },
   "dependencies": {
     "@backstage/version-bridge": "workspace:^",
+    "@internationalized/date": "^3.12.0",
     "@remixicon/react": "^4.6.0",
     "@tanstack/react-table": "^8.21.3",
     "clsx": "^2.1.1",