feat(05-02): install dnd-kit and create FieldPlacer component

- Install @dnd-kit/core@^6.3.1 and @dnd-kit/utilities@^3.2.2
- Create FieldPlacer.tsx with DndContext, draggable palette token, droppable PDF zone
- Implements Y-flip coordinate conversion (screenToPdfCoords / pdfToScreenCoords)
- Fetches existing fields from GET /api/documents/[id]/fields on mount
- Persists fields via PUT /api/documents/[id]/fields on every add/remove
- Renders placed fields as absolute-positioned blue-bordered overlays with remove button
- Default field size: 144x36 PDF points (2in x 0.5in at 72 DPI)

teressa-copeland-homes/package.json

@@ -16,6 +16,8 @@
   },
   "dependencies": {
     "@cantoo/pdf-lib": "^2.6.3",
+    "@dnd-kit/core": "^6.3.1",
+    "@dnd-kit/utilities": "^3.2.2",
     "@vercel/blob": "^2.3.1",
     "adm-zip": "^0.5.16",
     "bcryptjs": "^3.0.3",