feat: enhance medication reminder system with improved notifications and user settings updates

- Added new translation keys for empty and low stock notifications in both English and German.
- Implemented user authentication for planner routes and improved user settings loading.
- Separated empty and low stock medications for clearer notifications.
- Enhanced email notifications with detailed alerts for empty and low stock medications.
- Updated user settings in the database when reminders are sent for both intake and stock notifications.
- Improved form validation in the frontend with character limits and error messages.
- Added CSS styles for form validation feedback and character count display.

frontend/src/i18n/en.json

@@ -52,6 +52,8 @@
       "noRemindersNeeded": "no reminders needed",
       "needReorder": "{{count}} med needs reorder",
       "needReorder_other": "{{count}} meds need reorder",
+      "emptyStock": "{{count}} med is empty",
+      "emptyStock_other": "{{count}} meds are empty",
       "lowWarning": "{{count}} medication running low",
       "lowWarning_other": "{{count}} medications running low",
       "waitingFirstCheck": "waiting for first check",
@@ -277,6 +279,11 @@
     "loading": "Loading...",
     "sending": "Sending...",
     "saving": "Saving...",
+    "validation": {
+      "required": "This field is required",
+      "maxLength": "Maximum {{max}} characters ({{current}}/{{max}})",
+      "tooLong": "{{current}}/{{max}} characters"
+    },
     "saved": "Saved ✓",
     "save": "Save",
     "cancel": "Cancel",