fix(schema): enhance error messages with file path context

Improved ParseError variants to include specific file paths in IO and YAML parsing errors,
making debugging easier when files are missing or contain invalid content.

- Modified ParseError::Io to include path information
- Modified ParseError::Yaml to include path information
- Added read_file_with_path helper function for consistent error handling
- Updated all file reading operations to use new error format

Now errors clearly indicate which specific file caused the issue, e.g.:
- "IO error at /path/to/course.yml: No such file or directory"
- "YAML parse error at /path/to/stage.yml: invalid type: string, expected u32"

Author: wangeguo

Cargo.lock

@@ -8,7 +8,7 @@ resolver = "2"
 [package]
 name = "backend"
 description = "Backend API and services for StackClass"
-version = "1.0.0"
+version = "1.0.1"
 edition = "2024"
 
 default-run = "stackclass-server"

Cargo.toml

@@ -6,7 +6,7 @@
     "license": {
       "name": ""
     },
-    "version": "1.0.0"
+    "version": "1.0.1"
   },
   "paths": {
     "/v1/courses": {