feat: ship Rust login manager and GitLab release pipeline

Replace the legacy Go implementation as the production path, quarantine the reference tree, add deterministic release packaging and version metadata, and run verification through GitLab CI.

legacy/go/auth/utmpx.go

@@ -0,0 +1,77 @@
+// auth — UTMPX user accounting (glibc only).
+//
+// Mirrors vendor/src/auth/utmpx.rs.
+package auth
+
+/*
+#include <utmpx.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "utmpx_time.h"
+*/
+import "C"
+import (
+	"time"
+	"unsafe"
+)
+
+type UtmpxSession struct {
+	ok       bool
+	username string
+	tty      uint8
+}
+
+func AddUtmpx(user string, tty uint8, pid uint32) *UtmpxSession {
+	s := &UtmpxSession{username: user, tty: tty}
+
+	cUser := C.CString(user)
+	defer C.free(unsafe.Pointer(cUser))
+
+	var ut C.struct_utmpx
+	C.memset(unsafe.Pointer(&ut), 0, C.sizeof_struct_utmpx)
+
+	ut.ut_type = C.USER_PROCESS
+	ut.ut_pid = C.pid_t(pid)
+
+	n := len(user)
+	if n > 32 {
+		n = 32
+	}
+	for i := 0; i < n; i++ {
+		ut.ut_user[i] = C.char(user[i])
+	}
+
+	ttyCh := byte('0' + tty)
+	ut.ut_line[0] = 't'
+	ut.ut_line[1] = 't'
+	ut.ut_line[2] = 'y'
+	ut.ut_line[3] = C.char(ttyCh)
+	ut.ut_id[0] = C.char(ttyCh)
+
+	us := time.Now().UnixMicro()
+	C.latchd_set_utmpx_time(&ut, C.int64_t(us/1_000_000), C.int32_t(us%1_000_000))
+
+	C.setutxent()
+	C.pututxline(&ut)
+
+	s.ok = true
+	return s
+}
+
+func (s *UtmpxSession) Close() {
+	if !s.ok {
+		return
+	}
+
+	var ut C.struct_utmpx
+	C.memset(unsafe.Pointer(&ut), 0, C.sizeof_struct_utmpx)
+	ut.ut_type = C.DEAD_PROCESS
+
+	C.setutxent()
+	C.pututxline(&ut)
+	C.endutxent()
+
+	s.ok = false
+}