refactor: install shadcn/ui primitives (button, card, input, textarea, label, tabs, switch, dialog, alert-dialog, badge, separator, sonner)

Pinned the CLI to shadcn@2.3.0 rather than the latest (4.16.0): the
latest generation targets Tailwind v4-only syntax (bare-value parens
like `gap-(--card-spacing)`, the `in-*` variant, `--spacing()`) that
silently fails to compile under this project's Tailwind v3.4.6.
2.3.0 is the last CLI generation producing classic hsl(var(--x))
v3-compatible component output.

Swapped @radix-ui/react-icons for the already-installed lucide-react
in dialog.tsx, and dropped sonner's next-themes dependency (the app
has no dark-mode toggle, so Toaster is hardcoded to theme="light").

Old custom src/components/ui/Button.tsx, Card.tsx, and Field.tsx are
removed here; call sites are updated in the following commits.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

components.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://ui.shadcn.com/schema.json",
-  "style": "radix-nova",
+  "style": "new-york",
   "rsc": true,
   "tsx": true,
   "tailwind": {
@@ -10,16 +10,11 @@
     "cssVariables": true,
     "prefix": ""
   },
-  "iconLibrary": "lucide",
-  "rtl": false,
   "aliases": {
     "components": "@/components",
     "utils": "@/lib/utils",
     "ui": "@/components/ui",
     "lib": "@/lib",
     "hooks": "@/hooks"
-  },
-  "menuColor": "default",
-  "menuAccent": "subtle",
-  "registries": {}
+  }
 }