❇️ Add R language support

### Language Name

R

### Tree-Sitter Grammar

https://github.com/r-lib/tree-sitter-r

### I will work on this

Yes

### Additional Info (optional)

R is a widely-used programming language for statistical computing and data analysis. The tree-sitter-r grammar already has SPM support and includes comprehensive syntax highlighting queries.

This would enable R code editing with proper highlighting for functions, variables, operators (including R-specific `<-`, `<<-`, `|>`, pipe operators), keywords, and roxygen2 documentation comments (`#'`).

Implementation is complete and tested - works for extracting symbols by name.