SFTP shim: coerce vfs.readFile via normalizeVfsBytesForSftp before storing

handles; use f.buf == null instead of !f.buf so empty buffers/strings do not
force SSH_FX_FAILURE on READ. READ accepts Buffer, typed views, or string after
WRITE.

Earlier in this branch: enqueueSftpReply(reqid) + FAILURE on errors; REQUEST.READ
validation in vendor bare-ssh2; coerce typed arrays to Buffer in SFTP.data and
Protocol.channelData/channelExtData. CHANGELOG notes.

packages/bare-os-seeder/kernel/etc/bare-os/posix_utilities.json

@@ -1,7 +1,7 @@
 {
   "schema": 2,
   "profileId": "bare-os-posix-like",
-  "generatedAt": "2026-04-21T22:05:44.363Z",
+  "generatedAt": "2026-04-21T22:11:56.311Z",
   "note": "Sparse POSIX Issue 7 coverage hints for /bin utilities. Omitted command names are not yet profiled here.",
   "commandIndex": [
     {