feat(highlight): add markdown syntax highlighting with injection

Add tree-sitter-md for markdown parsing with injection support for
fenced code blocks. Code inside markdown code fences (```rust, ```bash,
etc.) is now fully syntax highlighted.

Key fix: Use `#set! injection.include-children` directive in the
injection query to override tree-sitter-md's internal tokenization
of code_fence_content, allowing proper language injection.

- Add tree-sitter-md v0.5.2 dependency
- Add Markdown variant to Language enum (md, markdown aliases)
- Create queries/md-highlights.scm (minimal markdown highlights)
- Create queries/md-injections.scm (with include-children directive)
- Add test: test_markdown_injection_rust

Cargo.lock

@@ -1531,6 +1531,7 @@ dependencies = [
  "tree-sitter-html",
  "tree-sitter-javascript",
  "tree-sitter-json",
+ "tree-sitter-md",
  "tree-sitter-nix",
  "tree-sitter-python",
  "tree-sitter-rust",
@@ -1809,6 +1810,16 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4ae62f7eae5eb549c71b76658648b72cc6111f2d87d24a1e31fa907f4943e3ce"
 
+[[package]]
+name = "tree-sitter-md"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2c96068626225a758ddb1f7cfb82c7c1fab4e093dd3bde464e2a44e8341f58f5"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "tree-sitter-nix"
 version = "0.3.0"

Cargo.toml

@@ -38,6 +38,7 @@ toml     = "0.8"
 
 # Diagram rendering
 mermaid-rs-renderer = { version = "0.1", default-features = false }
+tree-sitter-md      = "0.5.2"
 
 # Patch dagre_rust to fix unwrap on None bug
 [patch.crates-io]

docs/content/features/syntax-highlighting.md

@@ -12,7 +12,7 @@ sukr highlights code blocks at build time using Tree-sitter. No client-side Java
 
 Use fenced code blocks with a language identifier:
 
-````markdown
+````md
 ```rust
 fn main() {
     println!("Hello, world!");

queries/md-highlights.scm

@@ -0,0 +1,35 @@
+; Minimal markdown block highlighting - only capture outside code blocks
+; Removed all captures that could match inside code_fence_content
+
+(atx_heading (inline) @text.title)
+(setext_heading (paragraph) @text.title)
+
+[
+  (atx_h1_marker)
+  (atx_h2_marker)
+  (atx_h3_marker)
+  (atx_h4_marker)
+  (atx_h5_marker)
+  (atx_h6_marker)
+  (setext_h1_underline)
+  (setext_h2_underline)
+] @punctuation.special
+
+(fenced_code_block_delimiter) @punctuation.delimiter
+(info_string (language) @string)
+
+(link_title) @string
+(link_destination) @text.uri
+(link_label) @text.reference
+
+[
+  (list_marker_plus)
+  (list_marker_minus)
+  (list_marker_star)
+  (list_marker_dot)
+  (list_marker_parenthesis)
+  (thematic_break)
+] @punctuation.special
+
+(block_quote_marker) @punctuation.special
+(backslash_escape) @string.escape

queries/md-injections.scm

@@ -0,0 +1,7 @@
+; Markdown injection queries - testing include-children directive
+
+(fenced_code_block
+  (info_string
+    (language) @injection.language)
+  (code_fence_content) @injection.content
+  (#set! injection.include-children))

src/highlight.rs

@@ -77,6 +77,7 @@ pub enum Language {
     Html,
     JavaScript,
     Json,
+    Markdown,
     Nix,
     Python,
     Rust,
@@ -95,6 +96,7 @@ impl Language {
             "html" => Some(Language::Html),
             "javascript" | "js" => Some(Language::JavaScript),
             "json" => Some(Language::Json),
+            "markdown" | "md" => Some(Language::Markdown),
             "nix" => Some(Language::Nix),
             "python" | "py" => Some(Language::Python),
             "rust" | "rs" => Some(Language::Rust),
@@ -183,6 +185,15 @@ static JSON_CONFIG: LazyLock<HighlightConfiguration> = LazyLock::new(|| {
     )
 });
 
+static MARKDOWN_CONFIG: LazyLock<HighlightConfiguration> = LazyLock::new(|| {
+    make_config(
+        tree_sitter_md::LANGUAGE.into(),
+        "markdown",
+        include_str!("../queries/md-highlights.scm"),
+        include_str!("../queries/md-injections.scm"),
+    )
+});
+
 static NIX_CONFIG: LazyLock<HighlightConfiguration> = LazyLock::new(|| {
     make_config(
         tree_sitter_nix::LANGUAGE.into(),
@@ -238,6 +249,7 @@ fn get_config(lang: Language) -> &'static HighlightConfiguration {
         Language::Html => &HTML_CONFIG,
         Language::JavaScript => &JAVASCRIPT_CONFIG,
         Language::Json => &JSON_CONFIG,
+        Language::Markdown => &MARKDOWN_CONFIG,
         Language::Nix => &NIX_CONFIG,
         Language::Python => &PYTHON_CONFIG,
         Language::Rust => &RUST_CONFIG,
@@ -387,4 +399,29 @@ pkgs.stdenv.mkDerivation {
         // String content should be present
         assert!(html.contains("Hello from bash"));
     }
+
+    #[test]
+    fn test_markdown_injection_rust() {
+        // Markdown code block with embedded Rust should have full Rust highlighting
+        let md = "```rust\nfn main() {\n    println!(\"Hello\");\n}\n```";
+        let html = highlight_code(Language::Markdown, md);
+
+        // All Rust tokens should be highlighted
+        assert!(
+            html.contains("hl-keyword"),
+            "fn should be highlighted as keyword"
+        );
+        assert!(
+            html.contains("hl-function"),
+            "main/println should be highlighted as function"
+        );
+        assert!(
+            html.contains("hl-string"),
+            "string literal should be highlighted"
+        );
+        assert!(
+            html.contains("hl-punctuation-bracket"),
+            "brackets should be highlighted"
+        );
+    }
 }