Update pricing model to include half-year pricing and enhance validation

- Introduced a new pricing field, `PricePerConfigPerHalfYear`, to the `PricingSettings` model, allowing for more flexible pricing options.
- Updated the `UpdatePricingSettingsCommand` and its validator to include the new half-year pricing, ensuring proper validation against the quarterly and yearly rates.
- Modified the `PricingSettingsDto` and related frontend components to accommodate the new half-year pricing field, including validation logic to prevent pricing discrepancies.
- Enhanced API documentation and frontend forms to reflect the updated pricing structure and validation rules.

frontend/src/features/admin/pricing/PricingSettingsEditor.tsx

@@ -15,21 +15,38 @@ export function PricingSettingsEditor({ settings }: { settings: PricingSettingsD
   const [pricePerConfigPerQuarter, setPricePerConfigPerQuarter] = useState(
     settings.pricePerConfigPerQuarter != null ? String(settings.pricePerConfigPerQuarter) : '',
   )
+  const [pricePerConfigPerHalfYear, setPricePerConfigPerHalfYear] = useState(
+    settings.pricePerConfigPerHalfYear != null ? String(settings.pricePerConfigPerHalfYear) : '',
+  )
   const [pricePerConfigPerYear, setPricePerConfigPerYear] = useState(
     settings.pricePerConfigPerYear != null ? String(settings.pricePerConfigPerYear) : '',
   )
 
-  // Обе ставки — цена за конфиг в месяц; итог за год (ставка×12) не должен быть дешевле итога за
-  // квартал (ставка×3), иначе выгоднее купить "год" и не продлевать, чем платить за квартал.
+  // Все ставки — цена за конфиг в месяц; итог за более длинный период (ставка × месяцев) не должен
+  // быть дешевле итога за более короткий, иначе выгоднее купить длинный тариф и не продлевать.
+  const isHalfYearCheaperThanQuarter =
+    pricePerConfigPerQuarter !== '' &&
+    pricePerConfigPerHalfYear !== '' &&
+    Number(pricePerConfigPerHalfYear) * 6 < Number(pricePerConfigPerQuarter) * 3
+
+  const isYearCheaperThanHalfYear =
+    pricePerConfigPerHalfYear !== '' &&
+    pricePerConfigPerYear !== '' &&
+    Number(pricePerConfigPerYear) * 12 < Number(pricePerConfigPerHalfYear) * 6
+
   const isYearCheaperThanQuarter =
+    pricePerConfigPerHalfYear === '' &&
     pricePerConfigPerQuarter !== '' &&
     pricePerConfigPerYear !== '' &&
     Number(pricePerConfigPerYear) * 12 < Number(pricePerConfigPerQuarter) * 3
 
+  const hasInvalidCombo = isHalfYearCheaperThanQuarter || isYearCheaperThanHalfYear || isYearCheaperThanQuarter
+
   const mutation = useMutation({
     mutationFn: () =>
       updatePricingSettings(
         pricePerConfigPerQuarter === '' ? null : Number(pricePerConfigPerQuarter),
+        pricePerConfigPerHalfYear === '' ? null : Number(pricePerConfigPerHalfYear),
         pricePerConfigPerYear === '' ? null : Number(pricePerConfigPerYear),
       ),
     onSuccess: async () => {
@@ -58,6 +75,20 @@ export function PricingSettingsEditor({ settings }: { settings: PricingSettingsD
         />
         <p className="text-xs text-muted-foreground">{t('admin.pricing.pricePerConfigPerQuarterHint')}</p>
       </div>
+      <div className="flex flex-col gap-1.5">
+        <Label htmlFor="pricePerConfigPerHalfYear">{t('admin.pricing.pricePerConfigPerHalfYear')}</Label>
+        <Input
+          id="pricePerConfigPerHalfYear"
+          type="number"
+          min={0}
+          value={pricePerConfigPerHalfYear}
+          onChange={(e) => setPricePerConfigPerHalfYear(e.target.value)}
+        />
+        <p className="text-xs text-muted-foreground">{t('admin.pricing.pricePerConfigPerHalfYearHint')}</p>
+        {isHalfYearCheaperThanQuarter && (
+          <p className="text-xs text-red-600">{t('admin.pricing.halfYearCheaperThanQuarter')}</p>
+        )}
+      </div>
       <div className="flex flex-col gap-1.5">
         <Label htmlFor="pricePerConfigPerYear">{t('admin.pricing.pricePerConfigPerYear')}</Label>
         <Input
@@ -68,12 +99,15 @@ export function PricingSettingsEditor({ settings }: { settings: PricingSettingsD
           onChange={(e) => setPricePerConfigPerYear(e.target.value)}
         />
         <p className="text-xs text-muted-foreground">{t('admin.pricing.pricePerConfigPerYearHint')}</p>
+        {isYearCheaperThanHalfYear && (
+          <p className="text-xs text-red-600">{t('admin.pricing.yearCheaperThanHalfYear')}</p>
+        )}
         {isYearCheaperThanQuarter && (
           <p className="text-xs text-red-600">{t('admin.pricing.yearCheaperThanQuarter')}</p>
         )}
       </div>
       <div>
-        <Button type="submit" disabled={mutation.isPending || isYearCheaperThanQuarter}>
+        <Button type="submit" disabled={mutation.isPending || hasInvalidCombo}>
           {t('admin.roles.save')}
         </Button>
       </div>