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

internal/wol/wol.go

@@ -0,0 +1,80 @@
+package wol
+
+import (
+	"fmt"
+	"net"
+	"regexp"
+	"strings"
+	"time"
+)
+
+var macRegex = regexp.MustCompile(`^([0-9A-Fa-f]{2}[:-]){5}[0-9A-Fa-f]{2}$`)
+
+func ParseMAC(s string) ([6]byte, error) {
+	s = strings.ReplaceAll(s, "-", ":")
+	s = strings.ToLower(s)
+	if !macRegex.MatchString(s) {
+		return [6]byte{}, fmt.Errorf("invalid MAC address: %s", s)
+	}
+	parts := strings.Split(s, ":")
+	var mac [6]byte
+	for i := 0; i < 6; i++ {
+		var b int
+		if _, err := fmt.Sscanf(parts[i], "%x", &b); err != nil {
+			return [6]byte{}, fmt.Errorf("invalid MAC address: %s", s)
+		}
+		mac[i] = byte(b)
+	}
+	return mac, nil
+}
+
+func FormatMAC(mac [6]byte) string {
+	return fmt.Sprintf("%02x:%02x:%02x:%02x:%02x:%02x",
+		mac[0], mac[1], mac[2], mac[3], mac[4], mac[5])
+}
+
+func BuildMagicPacket(mac [6]byte) []byte {
+	packet := make([]byte, 6+16*6)
+	for i := 0; i < 6; i++ {
+		packet[i] = 0xFF
+	}
+	for i := 0; i < 16; i++ {
+		offset := 6 + i*6
+		copy(packet[offset:offset+6], mac[:])
+	}
+	return packet
+}
+
+func Send(addr string, mac [6]byte, broadcastAddr string) error {
+	packet := BuildMagicPacket(mac)
+
+	udpAddr := &net.UDPAddr{
+		IP:   net.IPv4bcast,
+		Port: 9,
+	}
+	if broadcastAddr != "" {
+		udpAddr.IP = net.ParseIP(broadcastAddr)
+		if udpAddr.IP == nil {
+			return fmt.Errorf("invalid broadcast address: %s", broadcastAddr)
+		}
+	}
+
+	conn, err := net.DialUDP("udp4", nil, udpAddr)
+	if err != nil {
+		return fmt.Errorf("creating UDP connection: %w", err)
+	}
+	defer conn.Close()
+
+	if err := conn.SetWriteDeadline(time.Now().Add(5 * time.Second)); err != nil {
+		return fmt.Errorf("setting broadcast mode: %w", err)
+	}
+
+	n, err := conn.Write(packet)
+	if err != nil {
+		return fmt.Errorf("sending magic packet: %w", err)
+	}
+	if n != len(packet) {
+		return fmt.Errorf("incomplete write: sent %d/%d bytes", n, len(packet))
+	}
+	return nil
+}