feat(tariffs): configurable purchase order for periods and packages

The order of enabled_periods (period tariffs) and traffic_packages
(traffic tariffs) is now the storefront order everywhere — both the
Telegram keyboard and the web app. Only new tariffs-config tariffs are
affected; legacy subscription/traffic options are untouched.

- Stop sorting periods and traffic packages in the web app plans
  serializer so it follows the configured order, matching the bot
  keyboards that already iterate the lists as-is.
- Preserve the row order through the admin draft (load and save) instead
  of sorting by months.
- Add a reusable Sortable component to the UI library (native HTML5
  drag & drop with a grip handle; bits-ui/shadcn have no such primitive)
  and use it to reorder period rows and traffic package rows in the
  tariff editor.

frontend/src/lib/admin/stores/tariffsStore.js

@@ -303,6 +303,24 @@ export function createTariffsStore({ api, onTariffsSaved, flash, at }) {
     }));
   }
 
+  function moveDraftRow(field, fromIndex, toIndex) {
+    state.update((s) => {
+      const rows = [...(s.tariffDraft[field] || [])];
+      if (
+        fromIndex === toIndex ||
+        fromIndex < 0 ||
+        toIndex < 0 ||
+        fromIndex >= rows.length ||
+        toIndex >= rows.length
+      ) {
+        return s;
+      }
+      const [moved] = rows.splice(fromIndex, 1);
+      rows.splice(toIndex, 0, moved);
+      return { ...s, tariffDraft: { ...s.tariffDraft, [field]: rows } };
+    });
+  }
+
   function updateState(updates) {
     state.update((s) => ({ ...s, ...updates }));
   }
@@ -326,5 +344,6 @@ export function createTariffsStore({ api, onTariffsSaved, flash, at }) {
     deleteTariff,
     addDraftRow,
     removeDraftRow,
+    moveDraftRow,
   };
 }

frontend/src/lib/admin/tariffDraft.js

@@ -69,6 +69,8 @@ export function rowsFromPackages(packageSet, currency, valueKey) {
 export function draftFromTariff(tariff, defaultCurrency = "rub") {
   const currency = normalizeCurrencyKey(defaultCurrency);
   const defaultPrices = tariff.prices?.[currency] || {};
+  // enabled_periods comes first so its order (the configured purchase order)
+  // is preserved; any extra price-only months are appended afterwards.
   const months = new Set([
     ...(tariff.enabled_periods || []),
     ...Object.keys(defaultPrices).map(Number),
@@ -77,7 +79,6 @@ export function draftFromTariff(tariff, defaultCurrency = "rub") {
   ]);
   const periodRows = [...months]
     .filter((month) => Number.isFinite(month) && month > 0)
-    .sort((a, b) => a - b)
     .map((month) => ({
       months: month,
       rub:
@@ -231,8 +232,7 @@ export function tariffFromDraft(draft, fallbackCurrency = "rub") {
         if (seenMonths.has(row.months)) return false;
         seenMonths.add(row.months);
         return true;
-      })
-      .sort((a, b) => a.months - b.months);
+      });
     tariff.monthly_gb = parseNumber(draft.monthly_gb, 0);
     tariff.enabled_periods = rows.map((row) => row.months);
     const defaultPrices = Object.fromEntries(rows.map((row) => [String(row.months), row.rub || 0]));

frontend/src/lib/components/ui/icons.js

@@ -29,6 +29,7 @@ export {
   FileText,
   Gift,
   Globe2,
+  GripVertical,
   Home,
   Info,
   Key,

frontend/src/lib/components/ui/index.js

@@ -11,6 +11,7 @@ export { default as RadioGroup } from "./radio-group.svelte";
 export { default as RadioGroupItem } from "./radio-group-item.svelte";
 export { default as RangeInput } from "./range-input.svelte";
 export { default as Skeleton } from "./skeleton.svelte";
+export { default as Sortable } from "./sortable.svelte";
 export { default as Spinner } from "./spinner.svelte";
 export { default as ScrollArea } from "./scroll-area.svelte";
 export { default as Textarea } from "./textarea.svelte";

frontend/src/lib/components/ui/sortable.svelte

@@ -0,0 +1,119 @@
+<script>
+  import { cn } from "$lib/utils.js";
+  import { GripVertical } from "./icons.js";
+
+  // Reusable drag-to-reorder list. bits-ui / shadcn-svelte have no sortable
+  // primitive, so this wraps native HTML5 drag & drop with a grip handle.
+  // Each item is rendered through the default (scoped) slot, which receives
+  // `item`, `index` and `dragging`. The slot content fills the row alongside
+  // the leading drag handle, so pass a grid `class` whose first column matches
+  // the handle width.
+  export let items = [];
+  export let onReorder = () => {};
+  export let getKey = (item) => item;
+  export let handleLabel = "Drag to reorder";
+  export let disabled = false;
+  let className = "";
+  export { className as class };
+  export let containerClass = "";
+
+  let dragIndex = null;
+  let dropIndex = null;
+
+  function handleDragStart(event, index) {
+    if (disabled) return;
+    dragIndex = index;
+    dropIndex = index;
+    if (event.dataTransfer) {
+      event.dataTransfer.effectAllowed = "move";
+      // Firefox requires data to be set for a drag to start.
+      event.dataTransfer.setData("text/plain", String(index));
+    }
+  }
+
+  function handleDragOver(event, index) {
+    if (dragIndex === null) return;
+    event.preventDefault();
+    if (event.dataTransfer) event.dataTransfer.dropEffect = "move";
+    dropIndex = index;
+  }
+
+  function handleDrop(event, index) {
+    if (dragIndex === null) return;
+    event.preventDefault();
+    if (dragIndex !== index) onReorder(dragIndex, index);
+    dragIndex = null;
+    dropIndex = null;
+  }
+
+  function reset() {
+    dragIndex = null;
+    dropIndex = null;
+  }
+</script>
+
+<div class={cn("ui-sortable", containerClass)} role="list">
+  {#each items as item, index (getKey(item, index))}
+    <div
+      class={cn("ui-sortable-item", className)}
+      class:is-dragging={dragIndex === index}
+      class:is-drop-target={dropIndex === index && dragIndex !== index}
+      role="listitem"
+      on:dragover={(event) => handleDragOver(event, index)}
+      on:drop={(event) => handleDrop(event, index)}
+      on:dragend={reset}
+    >
+      <button
+        type="button"
+        class="ui-sortable-handle"
+        draggable={!disabled}
+        aria-label={handleLabel}
+        title={handleLabel}
+        on:dragstart={(event) => handleDragStart(event, index)}
+      >
+        <GripVertical size={14} />
+      </button>
+      <slot {item} {index} dragging={dragIndex === index} />
+    </div>
+  {/each}
+</div>
+
+<style>
+  .ui-sortable {
+    display: grid;
+    gap: 8px;
+    min-width: 0;
+  }
+
+  .ui-sortable-item.is-dragging {
+    opacity: 0.5;
+  }
+
+  .ui-sortable-item.is-drop-target {
+    outline: 2px dashed var(--admin-accent, #4f8cff);
+    outline-offset: 2px;
+    border-radius: 8px;
+  }
+
+  .ui-sortable-handle {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 24px;
+    height: 100%;
+    padding: 0;
+    border: 0;
+    background: transparent;
+    color: var(--admin-muted, inherit);
+    cursor: grab;
+    touch-action: none;
+  }
+
+  .ui-sortable-handle:hover {
+    color: var(--admin-text, inherit);
+  }
+
+  .ui-sortable-handle:active {
+    cursor: grabbing;
+  }
+</style>