Address order: sequential, reverse or random, per subnet and pool

- Which never-used pool address a new client gets: sequential (the
  lowest, as before), reverse or random, in the settings, a subnet or
  a single pool (FIRST-LAST:ORDER). When no never-used address is left,
  the one free the longest, whatever the order; returning clients keep
  theirs.
- A subnet's pools are used in the order listed, or one at random
  weighted by its never-used addresses. Pools now keep the order they
  are given in (no more sorting by address).
- CLI --address-order and --pool-order; --add-pool of an existing range
  changes its order in place. Web UI: per-pool order and a move-up
  button, pool and address order on the subnet and settings pages.
- Kea's allocator: random is imported. Schema migration 5.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/state.go

@@ -25,7 +25,7 @@ func (s *Store) LoadState(ctx context.Context) (*model.State, error) {
 	if st.Settings.Options == nil {
 		st.Settings.Options = []model.OptionValue{}
 	}
-	rows, err := s.db.QueryContext(ctx, `SELECT id, name, interface, prefix, pools, lease_time, options, disabled, comment FROM subnets ORDER BY id`)
+	rows, err := s.db.QueryContext(ctx, `SELECT id, name, interface, prefix, pools, pool_order, address_order, lease_time, options, disabled, comment FROM subnets ORDER BY id`)
 	if err != nil {
 		return nil, err
 	}
@@ -34,7 +34,7 @@ func (s *Store) LoadState(ctx context.Context) (*model.State, error) {
 		sn := &model.Subnet{}
 		var prefix, pools, opts string
 		var disabled int
-		if err := rows.Scan(&sn.ID, &sn.Name, &sn.Interface, &prefix, &pools, &sn.LeaseTime, &opts, &disabled, &sn.Comment); err != nil {
+		if err := rows.Scan(&sn.ID, &sn.Name, &sn.Interface, &prefix, &pools, &sn.PoolOrder, &sn.AddressOrder, &sn.LeaseTime, &opts, &disabled, &sn.Comment); err != nil {
 			return nil, err
 		}
 		sn.Prefix, _ = netip.ParsePrefix(prefix)
@@ -146,10 +146,10 @@ func applyChange(ctx context.Context, tx *sql.Tx, c model.Change) error {
 		if err := json.Unmarshal(c.After, &sn); err != nil {
 			return err
 		}
-		_, err := tx.ExecContext(ctx, `INSERT INTO subnets (id, name, interface, prefix, pools, lease_time, options, disabled, comment) VALUES (?,?,?,?,?,?,?,?,?)
+		_, err := tx.ExecContext(ctx, `INSERT INTO subnets (id, name, interface, prefix, pools, pool_order, address_order, lease_time, options, disabled, comment) VALUES (?,?,?,?,?,?,?,?,?,?,?)
 			ON CONFLICT(id) DO UPDATE SET name = excluded.name, interface = excluded.interface, prefix = excluded.prefix, pools = excluded.pools,
-			lease_time = excluded.lease_time, options = excluded.options, disabled = excluded.disabled, comment = excluded.comment`,
-			sn.ID, sn.Name, sn.Interface, sn.Prefix.String(), jsonText(nonNil(sn.Pools)), sn.LeaseTime, jsonText(nonNilOpts(sn.Options)), boolInt(sn.Disabled), sn.Comment)
+			pool_order = excluded.pool_order, address_order = excluded.address_order, lease_time = excluded.lease_time, options = excluded.options, disabled = excluded.disabled, comment = excluded.comment`,
+			sn.ID, sn.Name, sn.Interface, sn.Prefix.String(), jsonText(nonNil(sn.Pools)), sn.PoolOrder, sn.AddressOrder, sn.LeaseTime, jsonText(nonNilOpts(sn.Options)), boolInt(sn.Disabled), sn.Comment)
 		return err
 	case model.KindReservation:
 		if c.After == nil {

internal/store/store.go

@@ -201,6 +201,11 @@ ALTER TABLE reservations ADD COLUMN disabled INTEGER NOT NULL DEFAULT 0;
 	// 4: when a lease's client last answered a ping.
 	`
 ALTER TABLE leases ADD COLUMN last_seen TEXT;
+`,
+	// 5: the order addresses are handed out in (a pool's own is in pools).
+	`
+ALTER TABLE subnets ADD COLUMN pool_order TEXT NOT NULL DEFAULT '';
+ALTER TABLE subnets ADD COLUMN address_order TEXT NOT NULL DEFAULT '';
 `,
 }