feat: add syntax highlighting for 9 additional languages

- Cargo.toml: Add tree-sitter grammars for Nix, Python, JavaScript,
  TypeScript, Go, C, CSS, HTML, YAML. Upgrade tree-sitter-highlight
  to 0.26 for language version 15 compatibility.

- src/highlight.rs: Add Language enum variants and get_config()
  match arms for all new languages. Update render() callback for
  0.26 API (writes attributes to buffer). Add tests for Nix and
  Python highlighting.

TOML excluded due to incompatible API (tree-sitter 0.20 vs 0.26).

src/highlight.rs

@@ -56,18 +56,36 @@ const HTML_ATTRS: &[&[u8]] = &[
 /// Supported languages for syntax highlighting.
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Language {
-    Rust,
     Bash,
+    C,
+    Css,
+    Go,
+    Html,
+    JavaScript,
     Json,
+    Nix,
+    Python,
+    Rust,
+    TypeScript,
+    Yaml,
 }
 
 impl Language {
     /// Parse a language identifier from a code fence.
     pub fn from_fence(lang: &str) -> Option<Self> {
         match lang.to_lowercase().as_str() {
-            "rust" | "rs" => Some(Language::Rust),
             "bash" | "sh" | "shell" | "zsh" => Some(Language::Bash),
+            "c" => Some(Language::C),
+            "css" => Some(Language::Css),
+            "go" | "golang" => Some(Language::Go),
+            "html" => Some(Language::Html),
+            "javascript" | "js" => Some(Language::JavaScript),
             "json" => Some(Language::Json),
+            "nix" => Some(Language::Nix),
+            "python" | "py" => Some(Language::Python),
+            "rust" | "rs" => Some(Language::Rust),
+            "typescript" | "ts" | "tsx" => Some(Language::TypeScript),
+            "yaml" | "yml" => Some(Language::Yaml),
             _ => None,
         }
     }
@@ -76,21 +94,66 @@ impl Language {
 /// Get highlight configuration for a language.
 fn get_config(lang: Language) -> HighlightConfiguration {
     let (language, name, highlights) = match lang {
-        Language::Rust => (
-            tree_sitter_rust::LANGUAGE.into(),
-            "rust",
-            tree_sitter_rust::HIGHLIGHTS_QUERY,
-        ),
         Language::Bash => (
             tree_sitter_bash::LANGUAGE.into(),
             "bash",
             tree_sitter_bash::HIGHLIGHT_QUERY,
         ),
+        Language::C => (
+            tree_sitter_c::LANGUAGE.into(),
+            "c",
+            tree_sitter_c::HIGHLIGHT_QUERY,
+        ),
+        Language::Css => (
+            tree_sitter_css::LANGUAGE.into(),
+            "css",
+            tree_sitter_css::HIGHLIGHTS_QUERY,
+        ),
+        Language::Go => (
+            tree_sitter_go::LANGUAGE.into(),
+            "go",
+            tree_sitter_go::HIGHLIGHTS_QUERY,
+        ),
+        Language::Html => (
+            tree_sitter_html::LANGUAGE.into(),
+            "html",
+            tree_sitter_html::HIGHLIGHTS_QUERY,
+        ),
+        Language::JavaScript => (
+            tree_sitter_javascript::LANGUAGE.into(),
+            "javascript",
+            tree_sitter_javascript::HIGHLIGHT_QUERY,
+        ),
         Language::Json => (
             tree_sitter_json::LANGUAGE.into(),
             "json",
             tree_sitter_json::HIGHLIGHTS_QUERY,
         ),
+        Language::Nix => (
+            tree_sitter_nix::LANGUAGE.into(),
+            "nix",
+            tree_sitter_nix::HIGHLIGHTS_QUERY,
+        ),
+        Language::Python => (
+            tree_sitter_python::LANGUAGE.into(),
+            "python",
+            tree_sitter_python::HIGHLIGHTS_QUERY,
+        ),
+        Language::Rust => (
+            tree_sitter_rust::LANGUAGE.into(),
+            "rust",
+            tree_sitter_rust::HIGHLIGHTS_QUERY,
+        ),
+        Language::TypeScript => (
+            tree_sitter_typescript::LANGUAGE_TYPESCRIPT.into(),
+            "typescript",
+            tree_sitter_typescript::HIGHLIGHTS_QUERY,
+        ),
+        Language::Yaml => (
+            tree_sitter_yaml::LANGUAGE.into(),
+            "yaml",
+            tree_sitter_yaml::HIGHLIGHTS_QUERY,
+        ),
     };
 
     let mut config = HighlightConfiguration::new(language, name, highlights, "", "")
@@ -111,8 +174,9 @@ pub fn highlight_code(lang: Language, source: &str) -> String {
     };
 
     let mut renderer = HtmlRenderer::new();
-    let result = renderer.render(highlights, source.as_bytes(), &|highlight| {
-        HTML_ATTRS.get(highlight.0).copied().unwrap_or(b"<span>")
+    let result = renderer.render(highlights, source.as_bytes(), &|highlight, buf| {
+        let attrs = HTML_ATTRS.get(highlight.0).copied().unwrap_or(b"");
+        buf.extend_from_slice(attrs);
     });
 
     match result {
@@ -139,6 +203,27 @@ mod tests {
         assert_eq!(Language::from_fence("bash"), Some(Language::Bash));
         assert_eq!(Language::from_fence("sh"), Some(Language::Bash));
         assert_eq!(Language::from_fence("json"), Some(Language::Json));
+        assert_eq!(Language::from_fence("nix"), Some(Language::Nix));
+        assert_eq!(Language::from_fence("python"), Some(Language::Python));
+        assert_eq!(Language::from_fence("py"), Some(Language::Python));
+        assert_eq!(
+            Language::from_fence("javascript"),
+            Some(Language::JavaScript)
+        );
+        assert_eq!(Language::from_fence("js"), Some(Language::JavaScript));
+        assert_eq!(
+            Language::from_fence("typescript"),
+            Some(Language::TypeScript)
+        );
+        assert_eq!(Language::from_fence("ts"), Some(Language::TypeScript));
+        assert_eq!(Language::from_fence("tsx"), Some(Language::TypeScript));
+        assert_eq!(Language::from_fence("go"), Some(Language::Go));
+        assert_eq!(Language::from_fence("golang"), Some(Language::Go));
+        assert_eq!(Language::from_fence("c"), Some(Language::C));
+        assert_eq!(Language::from_fence("yaml"), Some(Language::Yaml));
+        assert_eq!(Language::from_fence("yml"), Some(Language::Yaml));
+        assert_eq!(Language::from_fence("css"), Some(Language::Css));
+        assert_eq!(Language::from_fence("html"), Some(Language::Html));
         assert_eq!(Language::from_fence("unknown"), None);
     }
 
@@ -147,11 +232,8 @@ mod tests {
         let code = "fn main() { println!(\"hello\"); }";
         let html = highlight_code(Language::Rust, code);
 
-        // Should contain span elements with highlight classes
         assert!(html.contains("class=\"hl-"));
-        // Should contain the keyword "fn"
         assert!(html.contains("fn"));
-        // Should contain the string
         assert!(html.contains("hello"));
     }
 
@@ -164,6 +246,24 @@ mod tests {
         assert!(html.contains("echo"));
     }
 
+    #[test]
+    fn test_highlight_nix_code() {
+        let code = "{ pkgs, ... }: { environment.systemPackages = [ pkgs.vim ]; }";
+        let html = highlight_code(Language::Nix, code);
+
+        assert!(html.contains("class=\"hl-"));
+        assert!(html.contains("pkgs"));
+    }
+
+    #[test]
+    fn test_highlight_python_code() {
+        let code = "def hello():\n    print(\"world\")";
+        let html = highlight_code(Language::Python, code);
+
+        assert!(html.contains("class=\"hl-"));
+        assert!(html.contains("def"));
+    }
+
     #[test]
     fn test_html_escape_fallback() {
         let escaped = html_escape("<script>alert('xss')</script>");