fix(salary): show the sysselsättningsgrad product next to the run salary input (#1702)

A Discord report had a 10 % employee: typing 4 531 in the run gave a
453,10 kr gross, so the user typed 45 310 to get it right. The engine was
correct (grundlön = månadslön × sysselsättningsgrad / 100) but nothing on
the row said so; the formula only lived in Beräkningsdetaljer. Below
100 % the row now prints "× 10 % = 4 531 kr" under the monthly salary
(input and read-only shapes), and both employee forms explain under
Sysselsättningsgrad that the base salary is monthly salary × degree.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/(dashboard)/salary/employees/[id]/page.tsx

@@ -317,6 +317,7 @@ export default function EmployeeDetailPage({ params }: { params: Promise<{ id: s
               <div className="space-y-2">
                 <Label htmlFor="employment_degree">{t('form_employment_degree')}</Label>
                 <Input id="employment_degree" name="employment_degree" type="number" defaultValue={employee.employment_degree} min="1" max="100" disabled={!canWrite} />
+                <p className="text-xs text-muted-foreground">{t('form_employment_degree_hint')}</p>
               </div>
               <div className="space-y-2">
                 <Label htmlFor="hours_per_week">{t('form_hours_per_week')}</Label>