refactor: migrate src/shell/shell.ts from Bun.file() to statSync (#14134)

packages/opencode/src/shell/shell.ts

@@ -1,5 +1,6 @@
 import { Flag } from "@/flag/flag"
 import { lazy } from "@/util/lazy"
+import { Filesystem } from "@/util/filesystem"
 import path from "path"
 import { spawn, type ChildProcess } from "child_process"
 
@@ -43,7 +44,7 @@ export namespace Shell {
         // git.exe is typically at: C:\Program Files\Git\cmd\git.exe
         // bash.exe is at: C:\Program Files\Git\bin\bash.exe
         const bash = path.join(git, "..", "..", "bin", "bash.exe")
-        if (Bun.file(bash).size) return bash
+        if (Filesystem.stat(bash)?.size) return bash
       }
       return process.env.COMSPEC || "cmd.exe"
     }