Add git-like file commit API (#15978)

### What problem does this PR solve?

| # | Method | Endpoint | Description | Git Equivalent |
|---|--------|----------|-------------|----------------|
| 1 | `POST` | `/api/v1/{prefix}/{folder_id}/commits` | Create a
snapshot commit with file changes (add/modify/delete/rename) | `git add`
+ `git commit` |
| 2 | `GET` | `/api/v1/{prefix}/{folder_id}/commits` | List commit
history (paginated) | `git log` |
| 3 | `GET` | `/api/v1/{prefix}/{folder_id}/commits/{commit_id}` | Get
commit detail with file changes | `git show` |
| 4 | `GET` | `/api/v1/{prefix}/{folder_id}/commits/{commit_id}/files` |
List file changes in a commit | `git show --name-status` |
| 5 | `GET` |
`/api/v1/{prefix}/{folder_id}/commits/diff?from=...&to=...` | Compare
two commits and return differences | `git diff` |
| 6 | `GET` | `/api/v1/{prefix}/{folder_id}/changes` | Get uncommitted
changes (add/modify/delete) | `git status` |
| 7 | `GET` | `/api/v1/{prefix}/{folder_id}/commits/{commit_id}/tree` |
Get the folder tree snapshot at commit time | `git ls-tree` |
| 8 | `GET` |
`/api/v1/{prefix}/{folder_id}/commits/{commit_id}/files/{file_id}/content`
| Get a file's content as it existed in a specific commit | `git show
HEAD:file` |
| 9 | `GET` | `/api/v1/{prefix}/{file_id}/versions` | Get version
history for a specific file across all commits | `git log -- file` |

Where `{prefix}/{id}` can be:
- `folders/{folder_id}` — direct folder access
- `workspaces/{workspace_id}` — alias of `folders/{folder_id}`
- `datasets/{dataset_id}` — resolves to the dataset's folder
- `memories/{memory_id}` — resolves to the memory's folder
- `skills/{skill_id}` — resolves to the skill's folder

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

internal/dao/file_commit.go

@@ -0,0 +1,154 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package dao
+
+import (
+	"ragflow/internal/entity"
+	"strings"
+
+	"github.com/google/uuid"
+)
+
+// FileCommitDAO file commit data access object
+type FileCommitDAO struct{}
+
+// NewFileCommitDAO create file commit DAO
+func NewFileCommitDAO() *FileCommitDAO {
+	return &FileCommitDAO{}
+}
+
+// GetByID gets a file commit by ID
+func (dao *FileCommitDAO) GetByID(id string) (*entity.FileCommit, error) {
+	var commit entity.FileCommit
+	err := DB.Where("id = ?", id).First(&commit).Error
+	if err != nil {
+		return nil, err
+	}
+	return &commit, nil
+}
+
+// Create creates a new file commit record
+func (dao *FileCommitDAO) Create(commit *entity.FileCommit) error {
+	return DB.Create(commit).Error
+}
+
+// UpdateTreeState updates the tree_state field for a commit
+func (dao *FileCommitDAO) UpdateTreeState(id string, treeState string) error {
+	return DB.Model(&entity.FileCommit{}).Where("id = ?", id).Update("tree_state", treeState).Error
+}
+
+// GetLatestByFolderID gets the latest (most recent) commit for a folder
+func (dao *FileCommitDAO) GetLatestByFolderID(folderID string) (*entity.FileCommit, error) {
+	var commit entity.FileCommit
+	err := DB.Where("folder_id = ?", folderID).
+		Order("create_time DESC").
+		First(&commit).Error
+	if err != nil {
+		return nil, err
+	}
+	return &commit, nil
+}
+
+// allowedFileCommitSorts is the whitelist of safe column names for
+// ListByFolderID's orderBy parameter to prevent SQL injection.
+var allowedFileCommitSorts = map[string]string{
+	"create_time": "create_time",
+	"create_date": "create_date",
+	"update_time": "update_time",
+	"update_date": "update_date",
+}
+
+// ListByFolderID lists commits for a folder with pagination
+func (dao *FileCommitDAO) ListByFolderID(folderID string, page, pageSize int, orderBy string, desc bool) ([]*entity.FileCommit, int64, error) {
+	var commits []*entity.FileCommit
+	var total int64
+
+	query := DB.Model(&entity.FileCommit{}).Where("folder_id = ?", folderID)
+
+	if err := query.Count(&total).Error; err != nil {
+		return nil, 0, err
+	}
+
+	// Sanitize orderBy against whitelist; fall back to create_time.
+	safeCol, ok := allowedFileCommitSorts[orderBy]
+	if !ok {
+		safeCol = "create_time"
+	}
+
+	orderDirection := "DESC"
+	if !desc {
+		orderDirection = "ASC"
+	}
+
+	orderClause := safeCol + " " + orderDirection
+
+	if page > 0 && pageSize > 0 {
+		offset := (page - 1) * pageSize
+		if err := query.Order(orderClause).Offset(offset).Limit(pageSize).Find(&commits).Error; err != nil {
+			return nil, 0, err
+		}
+	} else {
+		if err := query.Order(orderClause).Find(&commits).Error; err != nil {
+			return nil, 0, err
+		}
+	}
+
+	return commits, total, nil
+}
+
+// FileCommitItemDAO file commit item data access object
+type FileCommitItemDAO struct{}
+
+// NewFileCommitItemDAO create file commit item DAO
+func NewFileCommitItemDAO() *FileCommitItemDAO {
+	return &FileCommitItemDAO{}
+}
+
+// Create creates a new file commit item record
+func (dao *FileCommitItemDAO) Create(item *entity.FileCommitItem) error {
+	return DB.Create(item).Error
+}
+
+// ListByCommitID lists all items for a commit
+func (dao *FileCommitItemDAO) ListByCommitID(commitID string) ([]*entity.FileCommitItem, error) {
+	var items []*entity.FileCommitItem
+	err := DB.Where("commit_id = ?", commitID).Order("create_time ASC").Find(&items).Error
+	return items, err
+}
+
+// ListByFileID lists all commit items for a specific file (for version history)
+func (dao *FileCommitItemDAO) ListByFileID(fileID string) ([]*entity.FileCommitItem, error) {
+	var items []*entity.FileCommitItem
+	err := DB.Where("file_id = ?", fileID).Order("create_time DESC").Find(&items).Error
+	return items, err
+}
+
+// GetByCommitIDAndFileID gets a single commit item by commit and file ID
+func (dao *FileCommitItemDAO) GetByCommitIDAndFileID(commitID, fileID string) (*entity.FileCommitItem, error) {
+	var item entity.FileCommitItem
+	err := DB.Where("commit_id = ? AND file_id = ?", commitID, fileID).First(&item).Error
+	if err != nil {
+		return nil, err
+	}
+	return &item, nil
+}
+
+// generateCommitUUID generates a UUID for commit/commit_item IDs
+func generateCommitUUID() string {
+	id := uuid.New().String()
+	return strings.ReplaceAll(id, "-", "")
+}