deka

Attaches the DekaScript language server (`dsc lsp`, stdio) to .ds and .dsx
buffers. The dsc binary is resolved with a managed search order:
explicit override > previously downloaded copy > dsc on PATH >
version-pinned, checksum-verified download. Highlighting is provided by
the tree-sitter parser (dekaruntime/tree-sitter-deka) via nvim-treesitter.