feat: 新增 Knowledge 知识库后端服务

- 添加 Knowledge 实体定义
- 添加 Knowledge 仓储层
- 添加 Knowledge 服务层

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/repository/knowledge_repo.go

@@ -0,0 +1,97 @@
+package repository
+
+import (
+	"x-agents/server/internal/model"
+
+	"gorm.io/gorm"
+)
+
+type KnowledgeRepository struct {
+	db *gorm.DB
+}
+
+func NewKnowledgeRepository(db *gorm.DB) *KnowledgeRepository {
+	return &KnowledgeRepository{db: db}
+}
+
+// Create 创建知识库
+func (r *KnowledgeRepository) Create(kb *model.KnowledgeBase) error {
+	return r.db.Create(kb).Error
+}
+
+// FindByID 根据ID查询
+func (r *KnowledgeRepository) FindByID(id string) (*model.KnowledgeBase, error) {
+	var kb model.KnowledgeBase
+	err := r.db.First(&kb, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &kb, nil
+}
+
+// FindAll 查询所有
+func (r *KnowledgeRepository) FindAll() ([]model.KnowledgeBase, error) {
+	var list []model.KnowledgeBase
+	err := r.db.Order("created_at DESC").Find(&list).Error
+	return list, err
+}
+
+// Update 更新知识库
+func (r *KnowledgeRepository) Update(id string, updates map[string]interface{}) error {
+	return r.db.Model(&model.KnowledgeBase{}).Where("id = ?", id).Updates(updates).Error
+}
+
+// Delete 删除知识库
+func (r *KnowledgeRepository) Delete(id string) error {
+	return r.db.Delete(&model.KnowledgeBase{}, "id = ?", id).Error
+}
+
+// ========== Document ==========
+
+// CreateDocument 创建文档
+func (r *KnowledgeRepository) CreateDocument(doc *model.KnowledgeDocument) error {
+	return r.db.Create(doc).Error
+}
+
+// FindDocumentByID 根据ID查询文档
+func (r *KnowledgeRepository) FindDocumentByID(id string) (*model.KnowledgeDocument, error) {
+	var doc model.KnowledgeDocument
+	err := r.db.First(&doc, "id = ?", id).Error
+	if err != nil {
+		return nil, err
+	}
+	return &doc, nil
+}
+
+// FindDocumentsByKBID 根据知识库ID查询文档
+func (r *KnowledgeRepository) FindDocumentsByKBID(kbID string, status string) ([]model.KnowledgeDocument, error) {
+	var list []model.KnowledgeDocument
+	query := r.db.Where("knowledge_base_id = ?", kbID).Order("uploaded_at DESC")
+	if status != "" && status != "all" {
+		query = query.Where("status = ?", status)
+	}
+	err := query.Find(&list).Error
+	return list, err
+}
+
+// UpdateDocument 更新文档
+func (r *KnowledgeRepository) UpdateDocument(id string, updates map[string]interface{}) error {
+	return r.db.Model(&model.KnowledgeDocument{}).Where("id = ?", id).Updates(updates).Error
+}
+
+// DeleteDocument 删除文档
+func (r *KnowledgeRepository) DeleteDocument(id string) error {
+	return r.db.Delete(&model.KnowledgeDocument{}, "id = ?", id).Error
+}
+
+// DeleteDocumentsByKBID 删除知识库下所有文档
+func (r *KnowledgeRepository) DeleteDocumentsByKBID(kbID string) error {
+	return r.db.Delete(&model.KnowledgeDocument{}, "knowledge_base_id = ?", kbID).Error
+}
+
+// CountDocumentsByKBID 统计知识库下文档数
+func (r *KnowledgeRepository) CountDocumentsByKBID(kbID string) (int64, error) {
+	var count int64
+	err := r.db.Model(&model.KnowledgeDocument{}).Where("knowledge_base_id = ?", kbID).Count(&count).Error
+	return count, err
+}