feat(ui): add description, tags, and metadata props to Header

Add three new props to the Header component:
- `tags`: renders a row of text/link items above the title, separated by
  3×3px circle dividers
- `description`: renders a markdown string below the title with inline
  link support via react-markdown
- `metadata`: renders key-value pairs below the description with 20px gaps

Also deprecates the `breadcrumbs` prop for future removal.

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

packages/ui/package.json

@@ -52,6 +52,7 @@
     "clsx": "^2.1.1",
     "react-aria": "~3.48.0",
     "react-aria-components": "~1.17.0",
+    "react-markdown": "^8.0.0",
     "react-stately": "~3.46.0",
     "use-sync-external-store": "^1.4.0"
   },