feat(v1.3): 管理员（打手）颜色，客户归属打手，日历/待办按颜色标识

1) 管理员颜色
- users 表新增 color；设置 → 管理员 每行一个颜色选择器，保存即生效
- 新建管理员自动从 8 色调色板分配，尽量不重复；支持 #RRGGBB 校验，非法值拒绝

2) 客户归属打手
- customers 表新增 assignee_id（可空，指向 users）
- 新建/编辑客户时可选择「归属打手」，客户详情页也能直接改派
- 语义：一个客户一个打手，该客户之后的所有单子都归这个打手
- 停用的账户不出现在打手候选里；未指派显示灰色「未指派」

3) 日历
- 每个日期格左侧新增 5px 竖条，按当天涉及的打手颜色等分显示（几种颜色几段）
- 竖条按“当天全部任务”去重计算，不受格内色签 3 条上限影响
- 未指派的任务用中性灰段落

4) 待办与大屏
- 「当日待完成」每条任务左侧 3px 打手色条 + 圆点色标 + 打手名字，未指派灰字
- 大屏：今日待打列表、热力格竖条、悬停浮层（新增 who / who_color 字段）统一使用同一套颜色
- 加急样式改为红底，避免与打手色左边框冲突

数据库兼容性：
- 只做加法：users.color、customers.assignee_id 两列；老库打开时自动 ALTER，可重复迁移
- 原有表结构、字段、页面接口不变；未指派的存量数据照常工作

测试：
- 新增单测：颜色自动分配/规范化/非法值拒绝、客户指派与取消、订阅联表带出打手、停用账户不进候选
- 旧库迁移测试扩展：老 users / customers 表自动补列并可写
- 功能验证 16 项（颜色保存、指派、详情展示、日历多色竖条分段、大屏列表与浮层接口）全部通过
- 原有 119 项验收回归全绿；go vet / go test ./... 通过；版本号 1.3.0

internal/web/handlers_customers.go

@@ -51,15 +51,17 @@ func (s *Server) handleCustomers(w http.ResponseWriter, r *http.Request) {
 type customerFormData struct {
 	Customer *store.Customer
 	IsNew    bool
+	Users    []store.User
 }
 
 func (s *Server) handleCustomerNewPage(w http.ResponseWriter, r *http.Request) {
 	p := s.newPage(r, "新建客户", "customers")
-	p.D = &customerFormData{Customer: &store.Customer{}, IsNew: true}
+	users, _ := s.db.ActiveUsers()
+	p.D = &customerFormData{Customer: &store.Customer{}, IsNew: true, Users: users}
 	s.render(w, r, "customer_form", p)
 }
 
-func readCustomerForm(r *http.Request) *store.Customer {
+func (s *Server) readCustomerForm(r *http.Request) *store.Customer {
 	return &store.Customer{
 		Tail:       strings.TrimSpace(r.PostFormValue("tail")),
 		Name:       strings.TrimSpace(r.PostFormValue("name")),
@@ -69,6 +71,7 @@ func readCustomerForm(r *http.Request) *store.Customer {
 		Tags:       normalizeTags(r.PostFormValue("tags")),
 		Source:     strings.TrimSpace(r.PostFormValue("source")),
 		Note:       strings.TrimSpace(r.PostFormValue("note")),
+		AssigneeID: int64(s.formInt(r, "assignee_id", 0)),
 	}
 }
 
@@ -104,10 +107,11 @@ func validateCustomer(c *store.Customer) string {
 }
 
 func (s *Server) handleCustomerCreate(w http.ResponseWriter, r *http.Request) {
-	c := readCustomerForm(r)
+	c := s.readCustomerForm(r)
 	p := s.newPage(r, "新建客户", "customers")
 	if msg := validateCustomer(c); msg != "" {
-		p.D = &customerFormData{Customer: c, IsNew: true}
+		users, _ := s.db.ActiveUsers()
+		p.D = &customerFormData{Customer: c, IsNew: true, Users: users}
 		s.fail(w, r, "customer_form", msg, p)
 		return
 	}
@@ -117,7 +121,8 @@ func (s *Server) handleCustomerCreate(w http.ResponseWriter, r *http.Request) {
 		if errors.Is(err, store.ErrDuplicate) {
 			msg = "该「尾号 + 姓名」的客户已存在，请直接搜索后追加订阅"
 		}
-		p.D = &customerFormData{Customer: c, IsNew: true}
+		users, _ := s.db.ActiveUsers()
+		p.D = &customerFormData{Customer: c, IsNew: true, Users: users}
 		s.fail(w, r, "customer_form", msg, p)
 		return
 	}
@@ -143,7 +148,7 @@ func (s *Server) handleCustomerUpdate(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
-	c := readCustomerForm(r)
+	c := s.readCustomerForm(r)
 	c.ID = id
 	p := s.newPage(r, "编辑客户", "customers")
 	if msg := validateCustomer(c); msg != "" {
@@ -179,6 +184,7 @@ type customerDetailData struct {
 	AdjSubColor map[int64]string
 	Checkins    []CheckinRow
 	Packages    []store.Package
+	Users       []store.User
 	Timeline    *Timeline
 	Extend      *ExtendPanel
 	TotalRemain string
@@ -208,7 +214,9 @@ func (s *Server) handleCustomerDetail(w http.ResponseWriter, r *http.Request) {
 	}
 	pauses, _ := s.db.PausesForSubs(ids)
 
+	users, _ := s.db.ActiveUsers()
 	data := &customerDetailData{
+		Users:       users,
 		Customer:    c,
 		Subs:        subViews(subs, today, warn),
 		Packages:    pkgs,
@@ -247,6 +255,31 @@ func (s *Server) handleCustomerDetail(w http.ResponseWriter, r *http.Request) {
 	s.render(w, r, "customer_detail", p)
 }
 
+// handleCustomerAssignee 从客户详情快速指派/取消打手。
+func (s *Server) handleCustomerAssignee(w http.ResponseWriter, r *http.Request) {
+	id := pathID(r)
+	userID := int64(s.formInt(r, "assignee_id", 0))
+	if err := s.db.SetCustomerAssignee(id, userID); err != nil {
+		s.redirect(w, r, "/customers/"+itoa(id), "指派失败："+err.Error())
+		return
+	}
+	c, _ := s.db.Customer(id)
+	word := "已取消指派"
+	if userID > 0 {
+		if u, err := s.db.UserByID(userID); err == nil {
+			name := u.DisplayName
+			if name == "" {
+				name = u.Username
+			}
+			word = "已指派给 " + name
+		}
+	}
+	if c != nil {
+		s.logOp(r, "指派打手", "customer", id, c.Tail+" "+c.Name+" "+word)
+	}
+	s.redirect(w, r, "/customers/"+itoa(id), word)
+}
+
 func (s *Server) handleSubCreate(w http.ResponseWriter, r *http.Request) {
 	customerID := pathID(r)
 	c, err := s.db.Customer(customerID)