refactor(packing): share the packing list logic between desktop and phone

usePackingItemActions, usePackingTemplates and usePackingImport take the
item, template and bulk import logic out of usePackingListPanel and
MPackingListTab, and the phone listsModel keeps only its priority
tokens.

When adding to a category the desktop looks for the placeholder in the
store and the phone in its rendered items. The desktop toasts on an
empty import, the phone runs one import at a time. The effects run in
the same order as before.

client/src/components/Packing/packingListModel.ts

@@ -0,0 +1,98 @@
+import type { PackingItem } from '../../types';
+import { PACKING_PLACEHOLDER_NAME } from './packingListPanel.constants';
+
+/**
+ * Pure view-model helpers for the packing list, shared by the desktop panel and
+ * the phone tab. No React, no side effects: grouping, filtering and counting
+ * only, so switching a filter on either surface produces the same buckets.
+ */
+
+export type PackingView = 'common' | 'personal';
+export type PackingStatusFilter = 'all' | 'open' | 'done';
+
+/** Three-tier sharing split (#858): Common = group pool, Personal = mine + shared-to-me. */
+export function packingViewItems(items: PackingItem[], view: PackingView): PackingItem[] {
+  return items.filter((i) => (view === 'common' ? !i.is_private : !!i.is_private));
+}
+
+/** Category display order = first-appearance order within the active view (stable colours). */
+export function packingCategoryOrder(viewItems: PackingItem[], defaultCategory: string): string[] {
+  const seen: string[] = [];
+  for (const item of viewItems) {
+    const cat = item.category || defaultCategory;
+    if (!seen.includes(cat)) seen.push(cat);
+  }
+  return seen;
+}
+
+export function packingStatusFiltered(items: PackingItem[], status: PackingStatusFilter): PackingItem[] {
+  if (status === 'open') return items.filter((i) => !i.checked);
+  if (status === 'done') return items.filter((i) => !!i.checked);
+  return items;
+}
+
+export interface PackingCategoryGroup {
+  category: string;
+  items: PackingItem[];
+}
+
+/** Groups the view+status filtered items by category, in first-encounter order. */
+export function groupPackingItems(
+  viewItems: PackingItem[],
+  status: PackingStatusFilter,
+  defaultCategory: string
+): PackingCategoryGroup[] {
+  const filtered = packingStatusFiltered(viewItems, status);
+  const order: string[] = [];
+  const byCategory = new Map<string, PackingItem[]>();
+  for (const item of filtered) {
+    const cat = item.category || defaultCategory;
+    let bucket = byCategory.get(cat);
+    if (!bucket) {
+      bucket = [];
+      byCategory.set(cat, bucket);
+      order.push(cat);
+    }
+    bucket.push(item);
+  }
+  return order.map((category) => ({ category, items: byCategory.get(category) as PackingItem[] }));
+}
+
+export interface PackingProgress {
+  checked: number;
+  total: number;
+  pct: number;
+}
+
+export function packingProgress(items: PackingItem[]): PackingProgress {
+  const checked = items.filter((i) => i.checked).length;
+  const total = items.length;
+  return { checked, total, pct: total > 0 ? Math.round((checked / total) * 100) : 0 };
+}
+
+/** "232 g" under 1000g, "1.2 kg" at/above, the phone's and the printout's weight label. */
+export function formatWeight(grams: number): string {
+  return grams >= 1000 ? `${(grams / 1000).toFixed(1)} kg` : `${Math.round(grams)} g`;
+}
+
+/** Weight an item contributes to a bag/total: unit weight times quantity. */
+export function packingItemWeight(item: Pick<PackingItem, 'weight_grams' | 'quantity'>): number {
+  return (item.weight_grams || 0) * (item.quantity || 1);
+}
+
+/**
+ * True when deleting `item` would empty its (custom) category: the row is then
+ * reset to the `...` placeholder instead of removed, so the category keeps its
+ * position and colour (#1289).
+ */
+export function isLastCustomItemInCategory(item: PackingItem, allItems: PackingItem[]): boolean {
+  return (
+    !!item.category &&
+    item.name !== PACKING_PLACEHOLDER_NAME &&
+    !allItems.some((i) => i.id !== item.id && i.category === item.category)
+  );
+}
+
+export function isPackingPlaceholder(item: Pick<PackingItem, 'name'>): boolean {
+  return item.name === PACKING_PLACEHOLDER_NAME;
+}