Remove ambiguous translations and fix invalid translations (#4841)

# Description of Changes
`i18next` allows this pattern for translations, which we use quite a few
times in our current translation files:

```json
{
  "a": {
     "b": "hello"
   },
   "a.b": "world"
}
```

This makes it ambiguous when selecting `a.b` which string will be
retrieved. We have seen issues in other languages in the current release
like this:

<img width="325" height="249" alt="image"
src="https://github.com/user-attachments/assets/f24a29f0-550f-49b8-b355-c5e5eb436558"
/>

because we are expecting this:

<img width="1022" height="210" alt="image"
src="https://github.com/user-attachments/assets/b6d5cdd4-96cd-4b2b-8f1a-465da8bf70c8"
/>

but the Spanish file has:

<img width="312" height="136" alt="image"
src="https://github.com/user-attachments/assets/1e13392c-8484-47d1-b0c4-19d52b3ea5eb"
/>

and no `removeDigitalSignature` key on its own. 

This PR resolves all of these ambiguities in the source by restructuring
all of the keys to uniquely target either an object or a string, not
both. It also adds a test which will fail on any keys with a `.` in
their name, therefore making it impossible to add anything ambiguous.

frontend/src/proprietary/components/shared/config/configSections/PeopleSection.tsx

@@ -668,7 +668,7 @@ export default function PeopleSection() {
             <Stack gap="md" align="center">
               <LocalIcon icon="person-add" width="3rem" height="3rem" style={{ color: 'var(--mantine-color-gray-6)' }} />
               <Text size="xl" fw={600} ta="center">
-                {t('workspace.people.inviteMembers', 'Invite Members')}
+                {t('workspace.people.inviteMembers.label', 'Invite Members')}
               </Text>
               {inviteMode === 'email' && (
                 <Text size="sm" c="dimmed" ta="center" px="md">