add ISO 8601 date picker, replace all native date inputs

custom DateInput component using react-day-picker + date-fns with
Calendar popover, always displays YYYY-MM-DD regardless of browser
locale. adds shadcn Popover and Calendar components. replaces all
<input type="date"> across process-stepper, contact-detail, contact-form

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
 	"name": "therapyfinder",
 	"private": true,
-	"version": "2026.03.11.2",
+	"version": "2026.03.11.3",
 	"type": "module",
 	"scripts": {
 		"dev": "vite",
@@ -21,10 +21,12 @@
 		"@tanstack/zod-form-adapter": "^0.42.1",
 		"class-variance-authority": "^0.7.1",
 		"clsx": "^2.1.1",
+		"date-fns": "^4.1.0",
 		"jspdf": "^4.2.0",
 		"lucide-react": "^0.577.0",
 		"radix-ui": "^1.4.3",
 		"react": "^19.2.4",
+		"react-day-picker": "^9.14.0",
 		"react-dom": "^19.2.4",
 		"tailwind-merge": "^3.5.0",
 		"tailwindcss": "^4.2.1",