feat: add Selenium Settings page to configure paymentGroupId per office

Adds a new Settings → Advanced → Selenium Settings page where the office
name (paymentGroupId) used in United/DentalHub portal dropdowns can be
configured without touching code. Previously hardcoded as "Summit Dental
Care"; now injected from DB into the three United workers at job dispatch.

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

packages/db/prisma/migrations/20260702000003_add_selenium_settings/migration.sql

@@ -0,0 +1,14 @@
+-- CreateTable
+CREATE TABLE "selenium_settings" (
+    "id" SERIAL NOT NULL,
+    "userId" INTEGER NOT NULL,
+    "paymentGroupId" TEXT NOT NULL DEFAULT '',
+
+    CONSTRAINT "selenium_settings_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "selenium_settings_userId_key" ON "selenium_settings"("userId");
+
+-- AddForeignKey
+ALTER TABLE "selenium_settings" ADD CONSTRAINT "selenium_settings_userId_fkey" FOREIGN KEY ("userId") REFERENCES "User"("id") ON DELETE CASCADE ON UPDATE CASCADE;