frontend: block past dates in appointment/invoice pickers; drop stale Settings Features

- Appointment date picker disables days before today.
- Invoice issue-date picker disables past days by default, with an opt-in
  "Back-date" checkbox for recording older invoices (edit mode keeps past
  dates). Added invoices.dialog.backdate to all locales.
- Removed the inert, outdated "Features" section (patient-owned storage /
  require signed toggles) from Settings and its now-unused i18n keys.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skills-lock.json

@@ -49,6 +49,24 @@
       "skillPath": "better-auth/emailAndPassword/SKILL.md",
       "computedHash": "747d7f73bd9e2ec5317b8ef88dc70f97df716d00e3d02de4051feebaa48b062d"
     },
+    "heroui-migration": {
+      "source": "heroui-inc/heroui",
+      "sourceType": "github",
+      "skillPath": "skills/heroui-migration/SKILL.md",
+      "computedHash": "9696b5cf0009120bfe03e00cc94c0e2defc1f5af981fc5bb10b1eeffa53e34cf"
+    },
+    "heroui-native": {
+      "source": "heroui-inc/heroui",
+      "sourceType": "github",
+      "skillPath": "skills/heroui-native/SKILL.md",
+      "computedHash": "d2fc03a13d03678d40799726a144ba72ba1cb08126176ddbf0a0461c901aef29"
+    },
+    "heroui-react": {
+      "source": "heroui-inc/heroui",
+      "sourceType": "github",
+      "skillPath": "skills/heroui-react/SKILL.md",
+      "computedHash": "c9e1bb41fbc3cee782faae08bd465ae05cd685a6ed7cc3392464fdf29b3ab467"
+    },
     "organization-best-practices": {
       "source": "better-auth/skills",
       "sourceType": "github",