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

cmd/server_main.go

@@ -232,6 +232,7 @@ func startServer(config *server.Config) {
 	searchBotHandler.SetAskService(service.NewAskService(chunkService, nil, 0, 0))
 	pluginHandler := handler.NewPluginHandler(service.NewPluginService())
 	modelHandler := handler.NewModelHandler(service.NewModelProviderService())
+	fileCommitHandler := handler.NewFileCommitHandler(service.NewFileCommitService())
 
 	// Dify retrieval handler
 	docDAO := dao.NewDocumentDAO()
@@ -262,7 +263,7 @@ func startServer(config *server.Config) {
 	adminRuntimeHandler := handler.NewAdminRuntimeHandler(adminRuntimeSelector)
 
 	// Initialize router
-	r := router.NewRouter(authHandler, userHandler, tenantHandler, documentHandler, datasetsHandler, systemHandler, knowledgebaseHandler, chunkHandler, llmHandler, chatHandler, chatSessionHandler, connectorHandler, searchHandler, fileHandler, memoryHandler, mcpHandler, skillSearchHandler, providerHandler, agentHandler, searchBotHandler, difyRetrievalHandler, pluginHandler, modelHandler, adminRuntimeHandler)
+	r := router.NewRouter(authHandler, userHandler, tenantHandler, documentHandler, datasetsHandler, systemHandler, knowledgebaseHandler, chunkHandler, llmHandler, chatHandler, chatSessionHandler, connectorHandler, searchHandler, fileHandler, memoryHandler, mcpHandler, skillSearchHandler, providerHandler, agentHandler, searchBotHandler, difyRetrievalHandler, pluginHandler, modelHandler, fileCommitHandler, adminRuntimeHandler)
 
 	// Create Gin engine
 	ginEngine := gin.New()