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

frontend/src/themes/theme-soft.css

@@ -53,4 +53,15 @@
   --radius-input: 6px;
   --radius-checkbox: 4px;
   --radius-pill: 9999px;
+
+  /* --- 7. CODE-SYNTAX-HIGHLIGHTING (VS Code Dark+) --- */
+  --code-keyword: #569cd6;
+  --code-string: #ce9178;
+  --code-number: #b5cea8;
+  --code-comment: #6a9955;
+  --code-property: #9cdcfe;
+  --code-function: #dcdcaa;
+  --code-type: #4ec9b0;
+  --code-punctuation: #d4d4d4;
+  --code-variable: #9cdcfe;
 }