show a specific error for dot-only usernames

Entering "." or ".." in the create user dialog showed the message listing periods as allowed characters, which didn't explain the rejection. The dialog now checks for dot-only names separately and shows its own message.

web/public/locales/en/views/settings.json

@@ -1054,6 +1054,7 @@
         "title": "Create New User",
         "desc": "Add a new user account and specify a role for access to areas of the Frigate UI.",
         "usernameOnlyInclude": "Username may only include letters, numbers, . or _",
+        "usernameOnlyDots": "Username cannot contain only periods",
         "confirmPassword": "Please confirm your password"
       },
       "deleteUser": {

web/src/components/overlay/CreateUserDialog.tsx

@@ -80,8 +80,11 @@ export default function CreateUserDialog({
       user: z
         .string()
         .min(1, t("users.dialog.form.usernameIsRequired"))
-        .regex(/^(?!\.+$)[A-Za-z0-9._]+$/, {
+        .regex(/^[A-Za-z0-9._]+$/, {
           message: t("users.dialog.createUser.usernameOnlyInclude"),
+        })
+        .regex(/[^.]/, {
+          message: t("users.dialog.createUser.usernameOnlyDots"),
         }),
       password: z
         .string()