fix: use local gem theme instead of remote_theme to fix missing CSS/JS

[BrewertonSantos]

O config usava remote_theme mas o plugin jekyll-remote-theme nao estava no Gemfile. Isso fazia o Jekyll ignorar o tema e gerar HTML puro sem CSS/JS. Corrigido usando theme: just-the-docs com o gem ja presente no Gemfile.

[Copilot]

Pull request overview

Adjusts the Jekyll site configuration to use the locally installed Just the Docs gem (instead of remote_theme) so the theme assets (CSS/JS) are applied during builds.

Changes:

• Switch _config.yml from remote_theme to theme: just-the-docs.
• Add webrick to the Gemfile for Ruby 3+ compatibility.
• Add a Gemfile.lock to lock Ruby gem dependencies.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
_config.yml	Uses the local just-the-docs theme gem instead of remote_theme.
Gemfile	Adds explicit webrick dependency.
Gemfile.lock	Locks dependencies for reproducible installs/builds.

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