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/ui/LocationEditForm.tsx

@@ -445,11 +445,20 @@ export const LocationEditForm: FC<LocationEditFormProps> = ({ location, yearMont
                                 <InfoBox>{t("update-scope-info")}</InfoBox>
                                 <fieldset className="fieldset mt-2 p-2">
                                     <legend className="fieldset-legend">{t("update-scope-legend")}</legend>
-                                    <select defaultValue="current" className="select input-bordered w-full" name="updateScope">
+                                    <select className="select input-bordered w-full" name="updateScope">
+                                        <option value="no-scope-selected">{t("update-option-placeholder")}</option>
                                         <option value="current">{t("update-current-month")}</option>
                                         <option value="subsequent">{t("update-subsequent-months")}</option>
                                         <option value="all">{t("update-all-months")}</option>
                                     </select>
+                                    <div id="updateScope-error" aria-live="polite" aria-atomic="true">
+                                        {state.errors?.updateScope &&
+                                            state.errors.updateScope.map((error: string) => (
+                                                <p className="mt-2 text-sm text-red-500" key={error}>
+                                                    {error}
+                                                </p>
+                                            ))}
+                                    </div>
                                 </fieldset>
                             </>
                         )}