feat: 双主题系统 — 编辑风 + 极简亮色

前端:
- 新增 Pinia theme store，localStorage 持久化，data-theme 切换
- App.vue: :root 新增 --font-*/--sidebar-* CSS 变量；新增 :root[data-theme=light] 完整配色（极简黑白金 + Noto Sans SC）
- DesktopLayout: 侧边栏 15 个变量化 + 顶栏主题切换按钮
- MobileLayout: 装饰色变量化
- Settings: 新增「界面主题」卡片
- 21 个组件 font-family 统一替换为 var(--font-*)
- 新增 utils/managerColor.ts — 12 色调色板 + 自适应文字色 + 后端自定义色优先
- WorkPlans/MiniBusiness/KeyVisits/CustomerManage: 客户经理标签色统一走共享工具
- UserManage: 编辑弹窗新增颜色选择器（仅 manager）
- LightBoard: 去标题星标图标
- ManagerWorkspace/WorkPlans/MiniBusiness/KeyVisits: 删除按钮改为实心红底白字

后端:
- User 模型新增 color 列 + lifespan 自动迁移
- users API 支持 color 字段读写
- UserOut schema 新增 color

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/utils/managerColor.ts

@@ -0,0 +1,55 @@
+import { reactive } from 'vue'
+
+// 12-color palettes — wide hue spacing for max distinction
+const COLORS_DARK = ['#C62828','#D84315','#EF6C00','#B8860B','#558B2F','#00897B','#0277BD','#C2185B','#4E342E','#00695C','#5D4037','#2E7D32']
+const COLORS_LIGHT = ['#FB7185','#FB923C','#FBBF24','#A3E635','#34D399','#2DD4BF','#38BDF8','#F472B6','#F97316','#84CC16','#22D3EE','#FDA4AF']
+
+// Reactive name→color overrides (populated from backend user.color)
+export const managerColorOverrides: Record<string, string> = reactive({})
+let loaded = false
+
+export async function loadManagerColors() {
+  if (loaded) return
+  try {
+    const { default: api } = await import('@/api/index')
+    const res = await api.get('/users/')
+    for (const u of res.data) {
+      if (u.color) managerColorOverrides[u.name] = u.color
+    }
+    loaded = true
+  } catch (_) {}
+}
+
+export function setManagerColorOverride(name: string, color: string | null) {
+  if (color) {
+    managerColorOverrides[name] = color
+  } else {
+    delete managerColorOverrides[name]
+  }
+}
+
+export function getManagerColor(name: string, isLight: boolean): string {
+  if (!name) return '#909399'
+  // Stored override takes priority
+  if (managerColorOverrides[name]) return managerColorOverrides[name]
+  // Fallback: deterministic hash from name
+  let h = 0
+  for (let i = 0; i < name.length; i++) h = name.charCodeAt(i) + ((h << 5) - h)
+  const colors = isLight ? COLORS_LIGHT : COLORS_DARK
+  return colors[Math.abs(h) % colors.length]
+}
+
+/** Return white or dark text color based on background luminance */
+export function getMgrTextColor(bgHex: string): string {
+  const r = parseInt(bgHex.slice(1, 3), 16)
+  const g = parseInt(bgHex.slice(3, 5), 16)
+  const b = parseInt(bgHex.slice(5, 7), 16)
+  const lum = 0.299 * r + 0.587 * g + 0.114 * b
+  return lum > 150 ? '#1A1A1A' : '#FFFFFF'
+}
+
+/** Return { background, color } style object for a manager tag */
+export function getMgrStyle(name: string, isLight: boolean) {
+  const bg = getManagerColor(name, isLight)
+  return { background: bg, color: getMgrTextColor(bg) }
+}