feat: coloration syntaxique via CSS classes (themeable)

Remplace les styles inline syntect par des classes CSS. Le CSS est
généré côté Rust (base16-ocean.dark) et injecté au démarrage via
get_syntax_highlight_css. Les thèmes peuvent surcharger .syntax-highlighting
et les classes de tokens. Supprime le lien CDN highlight.js inutilisé.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/src/infrastructure/comrak_renderer.rs

@@ -1,19 +1,16 @@
 use comrak::plugins::syntect::SyntectAdapterBuilder;
 use comrak::{markdown_to_html_with_plugins, Options, Plugins};
+use syntect::highlighting::ThemeSet;
+use syntect::html::{css_for_theme_with_class_style, ClassStyle};
 
 use crate::domain::MarkdownRenderer;
 
-pub struct ComrakRenderer {
-    pub theme: String,
-}
-
-pub struct ComrakPreviewRenderer {
-    pub theme: String,
-}
+pub struct ComrakRenderer;
+pub struct ComrakPreviewRenderer;
 
 impl MarkdownRenderer for ComrakRenderer {
     fn render(&self, content: &str) -> String {
-        let adapter = SyntectAdapterBuilder::new().theme(&self.theme).build();
+        let adapter = SyntectAdapterBuilder::new().css().build();
         let mut options = Options::default();
         options.extension.table = true;
         options.extension.strikethrough = true;
@@ -27,10 +24,60 @@ impl MarkdownRenderer for ComrakRenderer {
 
 impl MarkdownRenderer for ComrakPreviewRenderer {
     fn render(&self, content: &str) -> String {
-        let adapter = SyntectAdapterBuilder::new().theme(&self.theme).build();
+        let adapter = SyntectAdapterBuilder::new().css().build();
         let options = Options::default();
         let mut plugins = Plugins::default();
         plugins.render.codefence_syntax_highlighter = Some(&adapter);
         markdown_to_html_with_plugins(content, &options, &plugins)
     }
 }
+
+pub fn syntax_css_for_theme(syntect_theme_name: &str) -> String {
+    let ts = ThemeSet::load_defaults();
+    let theme = match ts.themes.get(syntect_theme_name) {
+        Some(t) => t,
+        None => return String::new(),
+    };
+    match css_for_theme_with_class_style(theme, ClassStyle::Spaced) {
+        Ok(css) => css.replace(".code {", ".syntax-highlighting {"),
+        Err(_) => String::new(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn render_outputs_syntax_highlighting_class() {
+        let r = ComrakRenderer;
+        let html = r.render("```rust\nfn main() {}\n```\n");
+        assert!(html.contains("syntax-highlighting"));
+    }
+
+    #[test]
+    fn render_outputs_classed_spans() {
+        let r = ComrakRenderer;
+        let html = r.render("```rust\nfn main() {}\n```\n");
+        assert!(html.contains("<span class="));
+    }
+
+    #[test]
+    fn syntax_css_known_theme_contains_wrapper() {
+        let css = syntax_css_for_theme("base16-ocean.dark");
+        assert!(!css.is_empty());
+        assert!(css.contains(".syntax-highlighting {"));
+    }
+
+    #[test]
+    fn syntax_css_known_theme_contains_token_rules() {
+        let css = syntax_css_for_theme("base16-ocean.dark");
+        assert!(css.contains("color:") || css.contains("color :"));
+    }
+
+    #[test]
+    fn syntax_css_unknown_theme_returns_empty() {
+        let css = syntax_css_for_theme("nonexistent-theme-xyz");
+        assert!(css.is_empty());
+    }
+}