feat: 购油方案 — 会员请求+老师定制+购油清单

后端:
- oil_plans/oil_plan_recipes 表
- 7个API: teachers列表、方案CRUD、配方增删、购油清单计算
- 购油清单自动算月消耗、瓶数、费用，交叉比对库存

前端:
- 会员端(库存页): 请求方案→选老师→描述需求；查看购油清单
- 老师端(用户管理): 接收请求→选配方+频率→激活方案
- plans store 管理状态

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/stores/plans.js

@@ -0,0 +1,62 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import { requestJSON, api } from '../composables/useApi'
+
+export const usePlansStore = defineStore('plans', () => {
+  const plans = ref([])
+  const teachers = ref([])
+  const shoppingList = ref([])
+
+  const activePlan = computed(() => plans.value.find(p => p.status === 'active'))
+  const pendingPlans = computed(() => plans.value.filter(p => p.status === 'pending'))
+
+  async function loadPlans() {
+    plans.value = await requestJSON('/api/oil-plans')
+  }
+
+  async function loadTeachers() {
+    teachers.value = await requestJSON('/api/teachers')
+  }
+
+  async function createPlan(healthDesc, teacherId) {
+    const res = await api('/api/oil-plans', {
+      method: 'POST',
+      body: JSON.stringify({ health_desc: healthDesc, teacher_id: teacherId }),
+    })
+    if (!res.ok) throw new Error('创建失败')
+    await loadPlans()
+    return res.json()
+  }
+
+  async function updatePlan(planId, data) {
+    await api(`/api/oil-plans/${planId}`, {
+      method: 'PUT',
+      body: JSON.stringify(data),
+    })
+    await loadPlans()
+  }
+
+  async function addRecipe(planId, recipeName, ingredients, timesPerMonth) {
+    await api(`/api/oil-plans/${planId}/recipes`, {
+      method: 'POST',
+      body: JSON.stringify({ recipe_name: recipeName, ingredients, times_per_month: timesPerMonth }),
+    })
+    await loadPlans()
+  }
+
+  async function removeRecipe(planId, recipeId) {
+    await api(`/api/oil-plans/${planId}/recipes/${recipeId}`, { method: 'DELETE' })
+    await loadPlans()
+  }
+
+  async function loadShoppingList(planId) {
+    shoppingList.value = await requestJSON(`/api/oil-plans/${planId}/shopping-list`)
+  }
+
+  return {
+    plans, teachers, shoppingList,
+    activePlan, pendingPlans,
+    loadPlans, loadTeachers, createPlan, updatePlan,
+    addRecipe, removeRecipe, loadShoppingList,
+  }
+})