revert: 删除购油方案功能，修复MyDiary模板错误

完全移除oil_plans相关代码：
- 后端: 7个API端点、2个数据库表
- 前端: plans store、Inventory方案UI、UserManagement方案编辑器
- UserMenu: 方案通知按钮
- 修复MyDiary.vue多余的section-card div导致的构建失败

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

frontend/src/stores/plans.js

@@ -1,65 +0,0 @@
-import { defineStore } from 'pinia'
-import { ref, computed } from 'vue'
-import { 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() {
-    const res = await api('/api/oil-plans')
-    if (res.ok) plans.value = await res.json()
-  }
-
-  async function loadTeachers() {
-    const res = await api('/api/teachers')
-    if (res.ok) teachers.value = await res.json()
-  }
-
-  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) {
-    const res = await api(`/api/oil-plans/${planId}/shopping-list`)
-    if (res.ok) shoppingList.value = await res.json()
-  }
-
-  return {
-    plans, teachers, shoppingList,
-    activePlan, pendingPlans,
-    loadPlans, loadTeachers, createPlan, updatePlan,
-    addRecipe, removeRecipe, loadShoppingList,
-  }
-})