fix: Use root path when building full destination

[fidian]

What is the purpose of this pull request?

• [X] Bug fix
• [ ] New Feature
• [ ] Documentation
• [ ] Other

Description

Previously this plugin would not do anything when you put your project's site files under a folder. See the root shared option. With this change, the user now can have source files in a folder that is not at the project root.

This may also fix FatehAK/vite-plugin-image-optimizer#30, since I am also using Vite 5.x.

Checks

• [X] PR adheres to the code style of this project
• [X] Related issues linked using fixes #number
• [X] Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• [ ] Lint and build have passed locally by running pnpm lint && pnpm build
• [X] Code changes have been verified in local
• [X] Documentation added/updated if necessary

Additional Context