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/models/schedule.go

@@ -0,0 +1,124 @@
+package models
+
+import (
+	"database/sql"
+	"time"
+)
+
+type Schedule struct {
+	ID          int64      `db:"id" json:"id"`
+	SyncPairID  int64      `db:"sync_pair_id" json:"sync_pair_id"`
+	CronExpr    string     `db:"cron_expr" json:"cron_expr"`
+	NextRunAt   *time.Time `db:"next_run_at" json:"next_run_at"`
+	Enabled     bool       `db:"enabled" json:"enabled"`
+	CreatedAt   time.Time  `db:"created_at" json:"created_at"`
+}
+
+type ScheduleRepository struct {
+	db *sql.DB
+}
+
+func NewScheduleRepository(db *sql.DB) *ScheduleRepository {
+	return &ScheduleRepository{db: db}
+}
+
+func (r *ScheduleRepository) Create(s *Schedule) (int64, error) {
+	res, err := r.db.Exec(`
+		INSERT INTO schedules (sync_pair_id, cron_expr, next_run_at, enabled)
+		VALUES (?, ?, ?, ?)`,
+		s.SyncPairID, s.CronExpr, s.NextRunAt, boolToInt(s.Enabled),
+	)
+	if err != nil {
+		return 0, err
+	}
+	return res.LastInsertId()
+}
+
+func (r *ScheduleRepository) GetAll() ([]Schedule, error) {
+	rows, err := r.db.Query(`
+		SELECT id, sync_pair_id, cron_expr, next_run_at, enabled, created_at
+		FROM schedules ORDER BY id`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var schedules []Schedule
+	for rows.Next() {
+		var s Schedule
+		var nextRun sql.NullTime
+		if err := rows.Scan(&s.ID, &s.SyncPairID, &s.CronExpr, &nextRun,
+			&s.Enabled, &s.CreatedAt); err != nil {
+			return nil, err
+		}
+		if nextRun.Valid {
+			s.NextRunAt = &nextRun.Time
+		}
+		s.Enabled = intToBool(intToInt(s.Enabled))
+		schedules = append(schedules, s)
+	}
+	return schedules, rows.Err()
+}
+
+func (r *ScheduleRepository) GetByID(id int64) (*Schedule, error) {
+	var s Schedule
+	var nextRun sql.NullTime
+	err := r.db.QueryRow(`
+		SELECT id, sync_pair_id, cron_expr, next_run_at, enabled, created_at
+		FROM schedules WHERE id = ?`, id).Scan(
+		&s.ID, &s.SyncPairID, &s.CronExpr, &nextRun, &s.Enabled, &s.CreatedAt)
+	if err != nil {
+		return nil, err
+	}
+	if nextRun.Valid {
+		s.NextRunAt = &nextRun.Time
+	}
+	s.Enabled = intToBool(intToInt(s.Enabled))
+	return &s, nil
+}
+
+func (r *ScheduleRepository) Update(s *Schedule) error {
+	_, err := r.db.Exec(`
+		UPDATE schedules SET sync_pair_id=?, cron_expr=?, next_run_at=?, enabled=?
+		WHERE id=?`,
+		s.SyncPairID, s.CronExpr, s.NextRunAt, boolToInt(s.Enabled), s.ID,
+	)
+	return err
+}
+
+func (r *ScheduleRepository) Delete(id int64) error {
+	_, err := r.db.Exec("DELETE FROM schedules WHERE id = ?", id)
+	return err
+}
+
+func (r *ScheduleRepository) GetEnabledDue(before time.Time) ([]Schedule, error) {
+	rows, err := r.db.Query(`
+		SELECT id, sync_pair_id, cron_expr, next_run_at, enabled, created_at
+		FROM schedules WHERE enabled = 1 AND next_run_at IS NOT NULL AND next_run_at <= ?
+		ORDER BY next_run_at`, before)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var schedules []Schedule
+	for rows.Next() {
+		var s Schedule
+		var nextRun sql.NullTime
+		if err := rows.Scan(&s.ID, &s.SyncPairID, &s.CronExpr, &nextRun,
+			&s.Enabled, &s.CreatedAt); err != nil {
+			return nil, err
+		}
+		if nextRun.Valid {
+			s.NextRunAt = &nextRun.Time
+		}
+		s.Enabled = true
+		schedules = append(schedules, s)
+	}
+	return schedules, rows.Err()
+}
+
+func (r *ScheduleRepository) UpdateNextRun(id int64, nextRun time.Time) error {
+	_, err := r.db.Exec("UPDATE schedules SET next_run_at = ? WHERE id = ?", nextRun, id)
+	return err
+}