🤖 Optimize Review tab syntax highlighting with CSS classes (#335)

## Problem
When `useInlineStyles={false}` is enabled in react-syntax-highlighter,
the library outputs CSS class names (`.token.keyword`, `.token.string`,
etc.) instead of computing inline styles at runtime. This reduces
JavaScript overhead, but requires actual CSS stylesheets to be loaded.

## Solution
- Generated `prism-syntax.css` from vscDarkPlus theme with backgrounds
removed
- Imported CSS in DiffRenderer.tsx where syntax highlighting is used
- CSS classes now available when `useInlineStyles={false}` prop is
active

## Testing
- ✅ All 661 tests pass
- ✅ TypeScript compilation successful
- Manual testing: Verify syntax highlighting still works in Review tab

## Related
- Builds on commit 1397430 which added `useInlineStyles={false}` prop
- Part of Review tab performance optimization work

_Generated with `cmux`_

Author: ammar-agent

scripts/generate_prism_css.ts

@@ -0,0 +1,93 @@
+#!/usr/bin/env bun
+
+/**
+ * Generates Prism CSS stylesheet from vscDarkPlus theme
+ * Used for syntax highlighting when react-syntax-highlighter has useInlineStyles={false}
+ * 
+ * Strips backgrounds to preserve diff backgrounds in Review tab
+ * Omits font-family and font-size to inherit from parent components
+ */
+
+import { vscDarkPlus } from "react-syntax-highlighter/dist/esm/styles/prism";
+import type { CSSProperties } from "react";
+
+const OUTPUT_PATH = "src/styles/prism-syntax.css";
+
+// Strip backgrounds like we do in syntaxHighlighting.ts
+const syntaxStyleNoBackgrounds: Record<string, CSSProperties> = {};
+for (const [key, value] of Object.entries(vscDarkPlus as Record<string, unknown>)) {
+  if (typeof value === "object" && value !== null) {
+    const { background, backgroundColor, ...rest } = value as Record<string, unknown>;
+    if (Object.keys(rest).length > 0) {
+      syntaxStyleNoBackgrounds[key] = rest as CSSProperties;
+    }
+  }
+}
+
+// Convert CSS properties object to CSS string
+function cssPropertiesToString(props: CSSProperties): string {
+  return Object.entries(props)
+    .filter(([key]) => {
+      // Skip font-family and font-size - we want to inherit these
+      return key !== "fontFamily" && key !== "fontSize";
+    })
+    .map(([key, value]) => {
+      // Convert camelCase to kebab-case
+      const cssKey = key.replace(/([A-Z])/g, "-$1").toLowerCase();
+      return `  ${cssKey}: ${value};`;
+    })
+    .join("\n");
+}
+
+// Generate CSS content
+function generateCSS(): string {
+  const lines: string[] = [
+    "/**",
+    " * Auto-generated Prism syntax highlighting styles",
+    " * Based on VS Code Dark+ theme with backgrounds removed",
+    " * Used when react-syntax-highlighter has useInlineStyles={false}",
+    " *",
+    " * Font family and size are intentionally omitted to inherit from parent.",
+    " * ",
+    " * To regenerate: bun run scripts/generate_prism_css.ts",
+    " */",
+    "",
+  ];
+
+  for (const [selector, props] of Object.entries(syntaxStyleNoBackgrounds)) {
+    const cssRules = cssPropertiesToString(props);
+    if (cssRules.trim().length > 0) {
+      // Handle selectors that need .token prefix
+      let cssSelector = selector;
+
+      // Add .token prefix for single-word selectors (token types)
+      if (!/[ >[\]:.]/.test(selector) && !selector.startsWith("pre") && !selector.startsWith("code")) {
+        cssSelector = `.token.${selector}`;
+      }
+
+      lines.push(`${cssSelector} {`);
+      lines.push(cssRules);
+      lines.push("}");
+      lines.push("");
+    }
+  }
+
+  return lines.join("\n");
+}
+
+async function main() {
+  console.log("Generating Prism CSS stylesheet...");
+
+  const css = generateCSS();
+
+  console.log(`Writing CSS to ${OUTPUT_PATH}...`);
+  await Bun.write(OUTPUT_PATH, css);
+
+  console.log("✓ Prism CSS generated successfully");
+}
+
+main().catch((error) => {
+  console.error("Error generating Prism CSS:", error);
+  process.exit(1);
+});
+

src/components/shared/DiffRenderer.tsx

@@ -10,6 +10,7 @@ import { Prism as SyntaxHighlighter } from "react-syntax-highlighter";
 import { syntaxStyleNoBackgrounds } from "@/styles/syntaxHighlighting";
 import { getLanguageFromPath } from "@/utils/git/languageDetector";
 import { Tooltip, TooltipWrapper } from "../Tooltip";
+import "@/styles/prism-syntax.css";
 
 // Shared type for diff line types
 export type DiffLineType = "add" | "remove" | "context" | "header";
@@ -159,6 +160,7 @@ const HighlightedContent = React.memo<{ code: string; language: string }>(({ cod
     <SyntaxHighlighter
       language={language}
       style={syntaxStyleNoBackgrounds}
+      useInlineStyles={false}
       PreTag="span"
       CodeTag="span"
       customStyle={{