fix: RunRemote SSH-to-source with pre-installed dest key, eliminating base64 round-trip

- Regenerate qnap.key and baby-nas.key to OpenSSH native format (387 bytes vs 119 PKCS8)
- Pre-install qnap.key on Baby NAS at /var/lib/syncserver/ssh/keys/
- Pre-populate Baby NAS known_hosts with Qnap host keys
- Simplify RunRemote: LXC SSH to Baby NAS, Baby NAS runs rsync with local qnap.key
- Remove wrapper script approach (rsync rejects remote-to-remote)

Makefile

@@ -1,5 +1,5 @@
 BINARY=syncserver
-VERSION?=1.0.27
+VERSION?=1.0.28
 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