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_time.h

@@ -0,0 +1,10 @@
+// Helper: assign seconds + microseconds to utmpx's ut_tv field.
+// The C compiler handles the type conversion, so this works whether
+// ut_tv is struct timeval (long tv_sec/tv_usec) or the compat struct
+// (__uint32_t tv_sec / __int32_t tv_usec).
+
+#include <stdint.h>
+static inline void latchd_set_utmpx_time(struct utmpx *ut, int64_t sec, int32_t usec) {
+	ut->ut_tv.tv_sec  = sec;
+	ut->ut_tv.tv_usec = usec;
+}