feat: complete SyncServer implementation

Full-stack Go monolith with embedded React frontend for orchestrating
rsync-over-SSH file synchronization with Wake-on-LAN support.

Features:
- JWT auth (HS256) with bcrypt password hashing
- CRUD for machines (with WoL config) and sync_pairs
- Ed25519 SSH key generation and known_hosts management
- WoL magic packet sender + TCP-connect waiter with backoff
- Sync engine: rsync subprocess, per-pair job queue, progress parsing
- Homebrew cron parser for scheduled syncs
- SSE stream for live job status (queued/waking_up/running/success/failed)
- React+TS+Vite+Tailwind SPA embedded via embed.FS
- Debian packaging with systemd unit, postinst/prerm/postrm

Tech stack:
- Go 1.22+ (CGO_ENABLED=0, pure SQLite via modernc.org/sqlite)
- chi router for HTTP API
- TypeScript + React 18 + Tailwind CSS frontend
- Cross-compiled to Linux amd64 for Proxmox LXC deployment

Tests: wol (MAC parsing, magic packet), syncengine/queue, scheduler/cron

packaging/debian/lib/systemd/system/syncserver.service

@@ -0,0 +1,27 @@
+[Unit]
+Description=SyncServer - File sync orchestrator with Wake-on-LAN and web UI
+Documentation=https://github.com/syncserver/syncserver
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=syncserver
+Group=syncserver
+ExecStart=/usr/bin/syncserver --config /etc/syncserver/config.yaml --data-dir /var/lib/syncserver
+Restart=on-failure
+RestartSec=5
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=syncserver
+
+# Hardening
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=strict
+ProtectHome=true
+ReadWritePaths=/var/lib/syncserver /run
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target