fix(s3): allow exists:false in head-object response contract (schema must match the missing-object output)

Author: waleedlatif1

apps/sim/lib/api/contracts/tools/aws/s3-head-object.ts

@@ -18,7 +18,7 @@ const S3HeadObjectSchema = z.object({
 const S3HeadObjectResponseSchema = z.object({
   success: z.literal(true),
   output: z.object({
-    exists: z.literal(true),
+    exists: z.boolean(),
     contentLength: z.number().nullable(),
     contentType: z.string().nullable(),
     etag: z.string().nullable(),