Add support for parsing frontmatter into custom structs

[Copilot]

This PR enables library users to parse frontmatter from both tasks and rules into their own custom structs with strongly-typed fields.

Changes Made

• New Method: Added Markdown.ParseFrontmatter(target any) error method that allows users to parse frontmatter into custom structs with YAML tags
• Input Validation: Validates nil target parameter for better error messages
• Comprehensive Tests: Added tests covering basic fields, nested selectors, array values, optional fields, and error cases
• Example Code: Added example usage demonstrating how to parse both task and rule frontmatter
• Documentation: Added inline godoc with usage examples

Example Usage

type TaskMetadata struct {
    TaskName    string `yaml:"task_name"`
    Resume      bool   `yaml:"resume"`
    Priority    string `yaml:"priority"`
}

result, err := cc.Run(context.Background(), "deploy")
if err != nil {
    log.Fatal(err)
}

// Parse task frontmatter
var taskMeta TaskMetadata
if err := result.Task.ParseFrontmatter(&taskMeta); err != nil {
    log.Fatal(err)
}

fmt.Printf("Task: %s, Priority: %s\n", taskMeta.TaskName, taskMeta.Priority)

// Parse rule frontmatter
for _, rule := range result.Rules {
    var ruleMeta struct {
        Language string `yaml:"language"`
    }
    if err := rule.ParseFrontmatter(&ruleMeta); err == nil {
        fmt.Printf("Language: %s\n", ruleMeta.Language)
    }
}

Implementation Details

• Method placed on Markdown type for better reusability across tasks and rules
• Uses existing YAML library to avoid adding new dependencies
• Marshal-unmarshal approach leverages existing project dependencies
• Comprehensive test coverage including edge cases

Testing

• ✅ All tests pass
• ✅ Code lints successfully (make lint)
• ✅ Build completes successfully
• ✅ Security scan completed with no issues (CodeQL)

Original prompt

The user of the library might want to have the front-matter from the task in their own struct. Can you provide a way to enable that?

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[alexec]

@copilot try again

[Copilot]

@copilot try again

I've implemented support for parsing task frontmatter into custom structs. The implementation includes:

1. New Result.ParseTaskFrontmatter(target any) error method
2. Comprehensive test coverage with multiple scenarios
3. Example code for library users
4. Nil validation for better error handling

Users can now parse task frontmatter like this:

type TaskMeta struct {
    TaskName string `yaml:"task_name"`
    Resume   bool   `yaml:"resume"`
    Priority string `yaml:"priority"`
}

var meta TaskMeta
err := result.ParseTaskFrontmatter(&meta)

All tests pass, code lints successfully, and no security vulnerabilities were found. (commits: 7248707, 7614126)