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- Removed the inert, outdated "Features" section (patient-owned storage /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>

.mcp.json

@@ -6,6 +6,16 @@
         "shadcn@latest",
         "mcp"
       ]
+    },
+    "XcodeBuildMCP": {
+      "type": "stdio",
+      "command": "npx",
+      "args": [
+        "-y",
+        "xcodebuildmcp@latest",
+        "mcp"
+      ],
+      "env": {}
     }
   }
-}
+}