refactor(cli): extract interactive menu into reusable module (#3)

Extract duplicate menu rendering logic from `index.ts` into a new `src/menu.ts` module, providing generic `selectOne` and `selectMany` functions. This reduces code duplication, improves maintainability, and adds consistent UI controls display across the commit flow and platform selection.

Reviewed-on: #3

src/pr.ts

@@ -151,7 +151,7 @@ export async function createPR(
     }
 
     const match = stdout.match(/(https?:\/\/[^\s]+)/);
-    return match ? match[1] : stdout.trim();
+    return match?.[1] ?? stdout.trim();
   }
 
   const args = [
@@ -180,5 +180,5 @@ export async function createPR(
   }
 
   const match = stdout.match(/(https?:\/\/[^\s]+)/);
-  return match ? match[1] : stdout.trim();
+  return match?.[1] ?? stdout.trim();
 }