fixed env and dark

[gafo25]

Changes

• Fixed error regarding reticulate. Added 2 if clauses to evaluate if RETICULATE_PYTHON exists and if pyenv exists. There was an error because reticulate tried to recreate pyenv but it is no needed if it already exists.
• Added dark mode. It works if your Windows 11 theme is dark theme. Replaced png to svg PHS logo. There are 2 logos depending on the theme.
• Added auto cleaning for knit cache and prerendered output