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/entity/file_commit.go

@@ -0,0 +1,108 @@
+//
+//  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 entity
+
+// FileCommit represents a snapshot commit for a workspace folder (like git commit).
+type FileCommit struct {
+	ID        string  `gorm:"column:id;primaryKey;size:32" json:"id"`
+	FolderID  string  `gorm:"column:folder_id;size:32;not null;index" json:"folder_id"`
+	ParentID  *string `gorm:"column:parent_id;size:32;index" json:"parent_id,omitempty"`
+	Message   string  `gorm:"column:message;size:512;not null;default:''" json:"message"`
+	AuthorID  string  `gorm:"column:author_id;size:32;not null;index" json:"author_id"`
+	FileCount int     `gorm:"column:file_count;default:0" json:"file_count"`
+	TreeState *string `gorm:"column:tree_state;type:longtext" json:"tree_state,omitempty"`
+	BaseModel
+}
+
+// TableName returns the table name for FileCommit model.
+func (FileCommit) TableName() string {
+	return "file_commit"
+}
+
+// FileCommitItem represents a single file change within a commit.
+type FileCommitItem struct {
+	ID          string  `gorm:"column:id;primaryKey;size:32" json:"id"`
+	CommitID    string  `gorm:"column:commit_id;size:32;not null;uniqueIndex:idx_commit_file" json:"commit_id"`
+	FileID      string  `gorm:"column:file_id;size:32;not null;uniqueIndex:idx_commit_file" json:"file_id"`
+	Operation   string  `gorm:"column:operation;size:16;not null;index" json:"operation"`
+	OldHash     *string `gorm:"column:old_hash;size:64;index" json:"old_hash,omitempty"`
+	NewHash     *string `gorm:"column:new_hash;size:64;index" json:"new_hash,omitempty"`
+	OldLocation *string `gorm:"column:old_location;size:255" json:"old_location,omitempty"`
+	NewLocation *string `gorm:"column:new_location;size:255" json:"new_location,omitempty"`
+	OldName     *string `gorm:"column:old_name;size:255" json:"old_name,omitempty"`
+	NewName     *string `gorm:"column:new_name;size:255" json:"new_name,omitempty"`
+	BaseModel
+}
+
+// TableName returns the table name for FileCommitItem model.
+func (FileCommitItem) TableName() string {
+	return "file_commit_item"
+}
+
+// TreeNode represents a file node in the commit tree state snapshot.
+type TreeNode struct {
+	ID          string      `json:"id"`
+	Name        string      `json:"name"`
+	Type        string      `json:"type"`        // "file" or "folder"
+	Hash        string      `json:"hash,omitempty"`
+	Location    string      `json:"location,omitempty"`
+	Size        int64       `json:"size,omitempty"`
+	Status      string      `json:"status"`       // "1" = active, "0" = deleted
+	Children    []*TreeNode `json:"children,omitempty"`
+}
+
+// FileChange represents a file change in a commit request.
+type FileChange struct {
+	FileID   string `json:"file_id"`
+	FileName string `json:"file_name"`
+	Operation string `json:"operation"` // "add", "modify", "delete", "rename"
+	Content  string `json:"content,omitempty"`
+	OldName  string `json:"old_name,omitempty"`
+	NewName  string `json:"new_name,omitempty"`
+}
+
+// CommitResponse is the API response for a commit.
+type CommitResponse struct {
+	ID        string  `json:"id"`
+	FolderID  string  `json:"folder_id"`
+	ParentID  *string `json:"parent_id,omitempty"`
+	Message   string  `json:"message"`
+	AuthorID  string  `json:"author_id"`
+	FileCount int     `json:"file_count"`
+	TreeState *string `json:"tree_state,omitempty"`
+	CreateTime *int64 `json:"create_time,omitempty"`
+}
+
+// DiffEntry represents a single diff entry between two commits.
+type DiffEntry struct {
+	FileID      string  `json:"file_id"`
+	FileName    string  `json:"file_name"`
+	Operation   string  `json:"operation"`
+	OldHash     *string `json:"old_hash,omitempty"`
+	NewHash     *string `json:"new_hash,omitempty"`
+	OldLocation *string `json:"old_location,omitempty"`
+	NewLocation *string `json:"new_location,omitempty"`
+}
+
+// VersionEntry represents a single version in a file's version history.
+type VersionEntry struct {
+	CommitID   string  `json:"commit_id"`
+	Operation  string  `json:"operation"`
+	Hash       string  `json:"hash"`
+	CreateTime *int64  `json:"create_time,omitempty"`
+	Message    string  `json:"message"`
+}