Fix MachineResponse: expose last_seen_at/created_at, clean status string

The status field was being decorated with "(last seen ...)" suffix
which broke frontend statusVariant() matching and prevented the
LastSeen column from showing the separate timestamp.

Changes:
- machineToResp() now returns clean status ("online"/"offline")
- MachineResponse includes last_seen_at and created_at as separate fields
- Fix whitespace typo in WakeCheckIntervalSeconds field

Makefile

@@ -1,5 +1,5 @@
 BINARY=syncserver
-VERSION?=1.0.41
+VERSION?=1.0.42
 GO?=go
 LDFLAGS=-s -w -X main.version=$(VERSION) -X main.commit=$(shell git rev-parse --short HEAD 2>/dev/null || echo unknown)
 BUILD_FLAGS=CGO_ENABLED=0