Enhance Release Workflow: Automated Changelog Management and Validation

[thomas-vilte]

Description

I implemented a more robust release workflow by automating the management of the [Unreleased] section in CHANGELOG.md. This PR introduces automatic migration of unreleased changes to the new version entry, comprehensive changelog validation, and a significantly improved preview UI for releases.

Key Changes

• Automated Changelog Migration: Implemented logic to automatically shift content from the [Unreleased] header to the new versioned header during the release process.
• Changelog Validation: Added a validation engine that checks for ISO 8601 dates, comparison links, and proper sectioning (###) to ensure "Keep a Changelog" compliance.
• Enhanced Release Preview: Refactored the preview command to display distinct sections for the Release Summary, CHANGELOG.md Preview, and GitHub Release Notes using a new PrintSectionHeader UI component.
• Resilient File I/O: Improved error handling for file operations with actionable user suggestions for permission and path issues.

Technical Impact

• Service Encapsulation: The ReleaseService now handles the full lifecycle of changelog formatting and validation, decoupling it from the command layer.
• Data Integrity: Regex-based validation prevents malformed changelogs from being committed to the repository.
• Testing Coverage: Introduced three new test suites covering unreleased section migration, validation logic, and semantic section rendering.

Fixes #81

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

I implemented comprehensive unit tests for the new service methods and manually verified the CLI output.

• Unit tests
• Integration tests
• Manual test: Verified the new CLI preview sections and file writing logic locally.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

🧪 Test Plan & Evidence

Suggested Manual Verification

• API/Backend: Attach JSON response or logs as evidence of correct behavior
• Performance: Ensure no significant latency increase
• Unit Tests: Run go test ./... and ensure all tests pass
• No Regressions: Verify that related features still work as expected