feat: add Caveman style under Fun category

Prompt: rewrite as a neanderthal caveman — broken grammar,
grunt words (ugh, oog), simplest names (big rock, fire stick),
dropped articles and conjugations, thoughts about food/shelter/danger,
raw emotional outbursts.

src/lib/styles.ts

@@ -157,6 +157,13 @@ export const styles: Style[] = [
     promptModifier:
       "Rewrite in Gen Z slang with no cap, fr, and modern internet vernacular",
   },
+  {
+    id: "caveman",
+    label: "Caveman",
+    categoryId: "fun",
+    promptModifier:
+      "Rewrite as a neanderthal caveman would speak — use broken grammar, grunt words like ugh and oog, refer to things by their simplest names like big rock and fire stick, shorten every word, drop articles and verb conjugations entirely, think only about food, shelter, and danger, and express emotions through raw outbursts",
+  },
 
   // Game of Thrones
   {