feat: require updateScope selection and improve form UX

Location Edit Form:
- Add validation requiring user to select update scope when editing locations
- Add "no-scope-selected" as placeholder option that must be replaced with valid choice
- Display validation error if user attempts to submit without selecting scope
- Clarify update scope options with improved wording (e.g., "ALL months (past and future)")

Bill Form UX:
- Add emoji icons (👤 tenant, 🔑 landlord) to "who bears cost" options for visual clarity

Translation updates:
- Add "update-scope-required" validation message (EN/HR)
- Improve clarity of update scope option labels
- Standardize Croatian terminology ("zadani" instead of "trenutni" for current month)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/app/lib/actions/locationActions.ts

@@ -27,6 +27,7 @@ export type State = {
         rentDueNotificationEnabled?: string[];
         rentDueDay?: string[];
         rentAmount?: string[];
+        updateScope?: string[];
     };
     message?:string | null;
 };
@@ -51,7 +52,7 @@ const FormSchema = (t:IntlTemplateFn) => z.object({
     rentDueDay: z.coerce.number().min(1).max(31).optional().nullable(),
     rentAmount: z.coerce.number().int(t("rent-amount-integer")).positive(t("rent-amount-positive")).optional().nullable(),
     addToSubsequentMonths: z.boolean().optional().nullable(),
-    updateScope: z.enum(["current", "subsequent", "all"]).optional().nullable(),
+    updateScope: z.enum(["no-scope-selected", "current", "subsequent", "all"]),
   })
   // dont include the _id field in the response
   .omit({ _id: true })
@@ -100,6 +101,16 @@ const FormSchema = (t:IntlTemplateFn) => z.object({
   }, {
     message: t("rent-amount-required"),
     path: ["rentAmount"],
+  })
+  .refine((data) => {
+    // When updateScope field is present (editing mode), user must select a valid option
+    if (data.updateScope === "no-scope-selected") {
+      return false;
+    }
+    return true;
+  }, {
+    message: t("update-scope-required"),
+    path: ["updateScope"],
   });
 
 /**
@@ -130,7 +141,7 @@ export const updateOrAddLocation = withUser(async (user:AuthenticatedUser, locat
         rentDueDay: formData.get('rentDueDay') || null,
         rentAmount: formData.get('rentAmount') || null,
         addToSubsequentMonths: formData.get('addToSubsequentMonths') === 'on',
-        updateScope: formData.get('updateScope') as "current" | "subsequent" | "all" | undefined,
+        updateScope: formData.get('updateScope') as "current" | "subsequent" | "all" | "",
     });
 
     // If form validation fails, return errors early. Otherwise, continue...