feat(ai): integrate templates and enforce strict JSON schemas

[thomas-vilte]

Description

I have integrated GitHub Issue and PR templates into the AI generation workflow. This allows the system to automatically detect and follow project-specific templates when generating content. Additionally, I implemented strict JSON schema enforcement in all AI prompts to ensure reliable parsing and prevent formatting issues. This PR also includes significant improvements to the template service to support Markdown files and PR-specific directories.

Fixes #64

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 have added and updated extensive unit tests across the AI and services packages to verify template detection, merging logic, and prompt rendering.

• Unit tests
• Integration tests
• Manual test: Verified that the CLI correctly identifies and uses templates located in .github/ISSUE_TEMPLATE and .github/PULL_REQUEST_TEMPLATE.

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

Closes #65

Closes #66