feat(06-01): add template API client functions and useTemplate hook

- Add ItemTier type and TemplateItem/TemplateDetail interfaces to api.ts
- Add item_tier field to BudgetItem interface
- Add template API object with get/updateName/addItem/updateItem/deleteItem/reorder
- Add generate function to budgets API object
- Create useTemplate hook with CRUD operations and reorder logic

frontend/src/hooks/useTemplate.ts

@@ -0,0 +1,98 @@
+import { useState, useEffect } from 'react'
+import {
+  template as templateApi,
+  categories as categoriesApi,
+  type TemplateDetail,
+  type TemplateItem,
+  type Category,
+  type ItemTier,
+} from '@/lib/api'
+
+export function useTemplate() {
+  const [templateDetail, setTemplateDetail] = useState<TemplateDetail | null>(null)
+  const [cats, setCats] = useState<Category[]>([])
+  const [loading, setLoading] = useState(true)
+
+  const fetchTemplate = async () => {
+    const data = await templateApi.get()
+    setTemplateDetail(data)
+  }
+
+  const fetchCategories = async () => {
+    const data = await categoriesApi.list()
+    setCats(data)
+  }
+
+  useEffect(() => {
+    const init = async () => {
+      try {
+        await Promise.all([fetchTemplate(), fetchCategories()])
+      } finally {
+        setLoading(false)
+      }
+    }
+    init()
+  }, [])
+
+  const addItem = async (data: {
+    category_id: string
+    item_tier: ItemTier
+    budgeted_amount?: number
+  }) => {
+    await templateApi.addItem(data)
+    await fetchTemplate()
+  }
+
+  const removeItem = async (itemId: string) => {
+    await templateApi.deleteItem(itemId)
+    await fetchTemplate()
+  }
+
+  const moveItem = async (itemId: string, direction: 'up' | 'down') => {
+    if (!templateDetail) return
+    const items = [...templateDetail.items].sort((a, b) => a.sort_order - b.sort_order)
+    const idx = items.findIndex((i) => i.id === itemId)
+    if (idx === -1) return
+    const swapIdx = direction === 'up' ? idx - 1 : idx + 1
+    if (swapIdx < 0 || swapIdx >= items.length) return
+
+    const current = items[idx]
+    const swap = items[swapIdx]
+    const reordered: { id: string; sort_order: number }[] = items.map((item) => {
+      if (item.id === current.id) return { id: item.id, sort_order: swap.sort_order }
+      if (item.id === swap.id) return { id: item.id, sort_order: current.sort_order }
+      return { id: item.id, sort_order: item.sort_order }
+    })
+
+    await templateApi.reorder(reordered)
+    await fetchTemplate()
+  }
+
+  const updateItem = async (
+    itemId: string,
+    data: { item_tier?: ItemTier; budgeted_amount?: number }
+  ) => {
+    await templateApi.updateItem(itemId, data)
+    await fetchTemplate()
+  }
+
+  return {
+    template: templateDetail,
+    categories: cats,
+    loading,
+    addItem,
+    removeItem,
+    moveItem,
+    updateItem,
+    refetch: fetchTemplate,
+  } as {
+    template: TemplateDetail | null
+    categories: Category[]
+    loading: boolean
+    addItem: (data: { category_id: string; item_tier: ItemTier; budgeted_amount?: number }) => Promise<void>
+    removeItem: (itemId: string) => Promise<void>
+    moveItem: (itemId: string, direction: 'up' | 'down') => Promise<void>
+    updateItem: (itemId: string, data: { item_tier?: ItemTier; budgeted_amount?: number }) => Promise<void>
+    refetch: () => Promise<void>
+  }
+}