feat(workspace): code block with language picker and live highlighting

frontend/src/themes/theme-light.css

@@ -52,4 +52,15 @@
   --radius-input: 2px;
   --radius-checkbox: 0px;
   --radius-pill: 9999px;
+
+  /* --- 7. CODE-SYNTAX-HIGHLIGHTING (VS Code Light+) --- */
+  --code-keyword: #0000ff;
+  --code-string: #a31515;
+  --code-number: #098658;
+  --code-comment: #008000;
+  --code-property: #0451a5;
+  --code-function: #795e26;
+  --code-type: #267f99;
+  --code-punctuation: #3b3b3b;
+  --code-variable: #001080;
 }