feat: import boilerplate components locally and unify frontmatter types

[ValentinBrclz]

Imported all components from astro-boilerplate-components directly into src/components and types to src/types to give users full control over styling, layout, and responsive behavior without depending on an external package.

Also standardized the type naming by renaming IFrontmatter → IFrontMatter and updated related imports
(including fixes in src/types/IFrontMatter.ts) for consistency across the codebase.

Context:

• Provides more flexibility for customization, particularly regarding layout responsiveness and component styling.
• Simplifies contributions by keeping all boilerplate logic in this repository, instead of the separate astro-boilerplate-components package, as suggested by the author.

This could also help to upgrade to Astro 5.x later on, without having to handle those components separately.

See #7 (it should help this issue, not sure if it solves the problem)
Fixes ixartz/astro-boilerplate-components#1