Add Tree-sitter grammar for Decodal

doc/manual/souce/development.md

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+# Development
+
+This document describes the development workflow for Decodal itself.
+
+## Rust checks
+
+Run the normal Rust checks from the repository root.
+
+```sh
+cargo fmt --check
+cargo test
+cargo check -p decodal-core --no-default-features
+nix flake check
+```
+
+Regex support is optional and should be tested explicitly when touched.
+
+```sh
+cargo test -p decodal-core --features regex
+cargo run -q -p decodal --features regex -- examples/regex/main.dcdl
+```
+
+## Tree-sitter grammar
+
+The Tree-sitter grammar is kept in:
+
+```text
+editors/tree-sitter-decodal/
+```
+
+Important files:
+
+```text
+editors/tree-sitter-decodal/grammar.js
+editors/tree-sitter-decodal/queries/highlights.scm
+editors/tree-sitter-decodal/queries/locals.scm
+editors/tree-sitter-decodal/corpus/basic.txt
+```
+
+The grammar is intended to be portable across editors such as Zed, Neovim, Helix, and Emacs.
+Zed support should consume this grammar rather than relying on a TextMate grammar.
+
+## Tree-sitter commands
+
+From the grammar directory:
+
+```sh
+cd editors/tree-sitter-decodal
+npm install
+npx tree-sitter generate
+npx tree-sitter test
+```
+
+To inspect a parse tree:
+
+```sh
+npx tree-sitter parse ../../examples/advanced/main.dcdl
+```
+
+The generated parser files under `editors/tree-sitter-decodal/src/` are committed so editor integrations can consume the grammar without regenerating it first.
+`node_modules/` is ignored and must not be committed.
+
+## Updating the grammar
+
+When the Decodal syntax changes:
+
+1. Update `grammar.js`.
+2. Run `npx tree-sitter generate`.
+3. Add or update corpus tests in `corpus/`.
+4. Update highlight queries in `queries/highlights.scm` if token names changed.
+5. Run `npx tree-sitter test`.
+6. Run Rust checks from the repository root if the language parser or examples also changed.
+
+## Development shell
+
+The Nix development shell includes Rust tooling, Node.js, and Tree-sitter CLI tooling.
+
+```sh
+nix develop
+```
+
+The shell provides:
+
+- `cargo`
+- `rustc`
+- `rustfmt`
+- `clippy`
+- `node`
+- `npm`
+- `tree-sitter`
+- `nixfmt`