feat: Implement validation for taskweaver_config.json (#511)

### Description
This PR addresses the `TODO` in
[taskweaver/utils/app_utils.py](cci:7://file:///c:/Users/singh/OneDrive/Documents/Open%20Source/TaskWeaver/taskweaver/utils/app_utils.py:0:0-0:0)
by implementing validation logic for the `taskweaver_config.json` file.

### Changes
- Implemented `json.load` to verify the configuration file contains
valid JSON.
- Added a check to ensure the root element is a dictionary
([dict](cci:1://file:///c:/Users/singh/OneDrive/Documents/Open%20Source/TaskWeaver/taskweaver/session/session.py:357:4-362:9)),
as expected for configuration files.
- Added error handling for `json.JSONDecodeError` and `OSError` to
prevent crashes when reading the file.

### Related Issues
Resolves TODO in `taskweaver/utils/app_utils.py`

Author: liqul

taskweaver/utils/app_utils.py

@@ -1,3 +1,4 @@
+import json
 from os import listdir, path
 from typing import Optional, Tuple
 
@@ -13,7 +14,14 @@ def validate_app_config(workspace: str) -> bool:
         config_path = path.join(workspace, "taskweaver_config.json")
         if not path.exists(config_path):
             return False
-        # TODO: read, parse and validate config
+        try:
+            with open(config_path, "r", encoding="utf-8") as f:
+                data = json.load(f)
+                # Config must be a dictionary (key-value pairs)
+                if not isinstance(data, dict):
+                    return False
+        except (json.JSONDecodeError, OSError):
+            return False
         return True
 
     def is_dir_valid(dir: str) -> bool: