fix: configure Quarto and install R package in pkgdown workflow

[aitorvv]

Description

This PR resolves the pkgdown website compilation errors on GitHub Actions by properly setting up the Quarto environment, which is required due to the presence of vignettes/biomass.qmd. Additionally, it cleans up duplicate entries in the _pkgdown.yml configuration.

Changes

• .github/workflows/pkgdown.yaml:
  • Added the quarto-dev/quarto-actions/setup@v2 step to install the Quarto CLI binary on the runner.
  • Added any::quarto explicitly to extra-packages in the setup-r-dependencies@v2 step, as suggested packages are not installed by default with needs: website.
  • Set install-quarto: true to ensure Quarto-specific dependencies are handled.
• _pkgdown.yml:
  • Removed duplicate listings of silv_predict_biomass_auto and silv_predict_biomass_components under the Predictions section.
  • Removed the duplicate listing of the deprecated silv_ntrees_ha function under the Stand density metrics section.

Verification

# Cargar la rama y validar que el paquete compile sin problemas
devtools::load_all()

# Ejecutar el check básico (sin viñetas debido a dependencias externas locales)
devtools::check(vignettes = FALSE)