suppress POSIX-shaped lint hits in libc FFI bindings

`lib/src/pty/ffi/libc.dart` carried 34 analyze infos:

- 26 × `non_constant_identifier_names` on struct field names
  (`msg_name`, `iov_base`, `msg_controllen`, etc.) that map 1:1
  to POSIX (`man 2 socketpair`, `recvmsg`, `iovec`, `msghdr`).
- 8 × `library_private_types_in_public_api` on the C / Dart
  function-signature typedefs (`_SocketpairC`, `_SocketpairDart`,
  etc.) consumed only by the `lookupFunction<...>()` calls in
  this same file.

Renaming the field names to lowerCamelCase would diverge from the
spec the file documents itself against; promoting the typedefs to
public would just add noise to the import surface. This is the
textbook FFI-binding case where the lints work against the file's
purpose.

Adds a file-wide `// ignore_for_file:` directive — explicitly
approved per the no-lint-suppression rule, with the reason
written inline above the directive so a future reader can
re-evaluate it.

Project analyze drops 65 → 31 issues.

Co-Authored-By: Claude <noreply@anthropic.com>

.pql/pql-plan.json

@@ -1,5 +1,5 @@
 {
-  "exported_at": "2026-05-06T21:46:24Z",
+  "exported_at": "2026-05-06T21:46:36Z",
   "decisions": [
     {
       "id": "D-1",

lib/src/pty/ffi/libc.dart

@@ -10,6 +10,24 @@
 /// set against the Win32 API (named pipes instead of unix sockets).
 library;
 
+// File-wide analyzer exceptions, with reason — see CLAUDE.md
+// no-lint-suppression rule. These are the textbook FFI-binding
+// case where the lints work against the file's purpose:
+//
+// * `non_constant_identifier_names` — struct field names map 1:1
+//   to POSIX (`man 2 socketpair`, `recvmsg`, `iovec`, `msghdr`).
+//   Keeping snake_case makes the code greppable against the spec
+//   and the field offsets readable next to the C ABI. Dart FFI
+//   layout depends on declaration order + types, not names, so
+//   this is purely a readability call.
+// * `library_private_types_in_public_api` — the C / Dart function-
+//   signature typedefs (`_SocketpairC`, `_SocketpairDart`, etc.)
+//   are implementation details consumed only by the public
+//   `lookupFunction<...>()` calls in this file. Promoting them
+//   to public would just add noise to the import surface.
+//
+// ignore_for_file: non_constant_identifier_names, library_private_types_in_public_api
+
 import 'dart:ffi' as ffi;
 import 'dart:io' show Platform;