feat: 配置列表分页与钉钉机器人分钟级排队限流

统一 sources/templates/channels/rules 列表为分页响应，避免配置增多时全量返回；按钉钉 access_token 限制每分钟发送并在超限时等待下一分钟，降低触发官方封禁风险。

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/store/page.go

@@ -0,0 +1,22 @@
+package store
+
+// PageFilter is the shared pagination query for list endpoints.
+type PageFilter struct {
+	Page     int `form:"page"`
+	PageSize int `form:"page_size"`
+}
+
+// Normalize applies defaults: page=1, page_size=20.
+func (p *PageFilter) Normalize() {
+	if p.Page <= 0 {
+		p.Page = 1
+	}
+	if p.PageSize <= 0 {
+		p.PageSize = 20
+	}
+}
+
+// Offset returns the SQL OFFSET for the current page.
+func (p PageFilter) Offset() int {
+	return (p.Page - 1) * p.PageSize
+}