feat(api): Add image multimodal support for LLMNode (#17372)

Enhance `LLMNode` with multimodal capability, introducing support for
image outputs.

This implementation extracts base64-encoded images from LLM responses,
saves them to the storage service, and records the file metadata in the
`ToolFile` table. In conversations, these images are rendered as
markdown-based inline images.
Additionally, the images are included in the LLMNode's output as
file variables, enabling subsequent nodes in the workflow to utilize them.

To integrate file outputs into workflows, adjustments to the frontend code
are necessary.

For multimodal output functionality, updates to related model configurations
are required. Currently, this capability has been applied exclusively to
Google's Gemini models.

Close #15814.

Signed-off-by: -LAN- <laipz8200@outlook.com>
Co-authored-by: -LAN- <laipz8200@outlook.com>

api/controllers/files/tool_files.py

@@ -4,7 +4,9 @@ from werkzeug.exceptions import Forbidden, NotFound
 
 from controllers.files import api
 from controllers.files.error import UnsupportedFileTypeError
+from core.tools.signature import verify_tool_file_signature
 from core.tools.tool_file_manager import ToolFileManager
+from models import db as global_db
 
 
 class ToolFilePreviewApi(Resource):
@@ -19,17 +21,14 @@ class ToolFilePreviewApi(Resource):
         parser.add_argument("as_attachment", type=bool, required=False, default=False, location="args")
 
         args = parser.parse_args()
-
-        if not ToolFileManager.verify_file(
-            file_id=file_id,
-            timestamp=args["timestamp"],
-            nonce=args["nonce"],
-            sign=args["sign"],
+        if not verify_tool_file_signature(
+            file_id=file_id, timestamp=args["timestamp"], nonce=args["nonce"], sign=args["sign"]
         ):
             raise Forbidden("Invalid request.")
 
         try:
-            stream, tool_file = ToolFileManager.get_file_generator_by_tool_file_id(
+            tool_file_manager = ToolFileManager(engine=global_db.engine)
+            stream, tool_file = tool_file_manager.get_file_generator_by_tool_file_id(
                 file_id,
             )
 

api/controllers/files/upload.py

@@ -53,7 +53,7 @@ class PluginUploadFileApi(Resource):
             raise Forbidden("Invalid request.")
 
         try:
-            tool_file = ToolFileManager.create_file_by_raw(
+            tool_file = ToolFileManager().create_file_by_raw(
                 user_id=user.id,
                 tenant_id=tenant_id,
                 file_binary=file.read(),