feat: Tree-sitter grammar (Neovim, Helix, Zed)

[dean0x]

Summary

Create a tree-sitter-mds grammar that extends Markdown parsing with MDS-specific syntax nodes. This provides structural parsing for editors that use Tree-sitter (Neovim, Helix, Zed), enabling code folding, text object selections, indentation rules, and precise highlighting.

Motivation

Tree-sitter grammars provide deeper editor integration than TextMate grammars: structural navigation (jump to matching @end), code folding (@if...@end blocks), text objects (select entire @define block), and indent/dedent rules. This is the standard for Neovim, Helix, and Zed users.

Scope

• A tree-sitter-mds grammar (C, generated from grammar.js)
• Parse nodes for all MDS directives: import, export, define, if_block, for_block, include, extends, block, message
• Interpolation nodes: interpolation, function_call, member_access
• Highlight queries (highlights.scm)
• Fold queries (folds.scm)
• Indent queries (indents.scm)
• Text object queries (textobjects.scm) for Neovim
• Published to the tree-sitter grammar registry

Design Considerations

• Tree-sitter MDS grammar should extend tree-sitter-markdown as an injection (MDS nodes injected into Markdown parse tree)
• The grammar must handle MDS-in-Markdown (.md files with type: mds frontmatter) and standalone .mds files
• Neovim integration via nvim-treesitter parser config
• Helix and Zed pick up grammars from the tree-sitter registry automatically
• Repo: separate tree-sitter-mds repository (tree-sitter convention)

Acceptance Criteria

• tree-sitter-mds grammar parses all MDS syntax constructs
• Highlight, fold, indent, and textobject queries provided
• Works as Markdown injection (preserves Markdown parsing)
• Neovim integration tested with nvim-treesitter
• Published to tree-sitter grammar registry
• Corpus test suite covering all directive types