Update git-worktree-create to use worktrees directory at sibling level

.opencode/tools/git-worktree-create.ts

@@ -9,7 +9,7 @@ export default tool({
   },
   async execute(args) {
     const worktreeDir = args.directory || args.branch
-    const result = await $`git worktree add ../${worktreeDir} ${args.branch}`.text()
+    const result = await $`git worktree add ../worktrees/${worktreeDir} ${args.branch}`.text()
     return result.trim()
   },
 })