Add AmneziaWG 3.1 support with key reissue

Protocol generation is now derived from awg1.conf rather than stored: an
interface speaks 3.1 when HeaderProtectionKey is set and 2.0 otherwise. The
3.0/3.1-only keys (HeaderProtectionKey, ContentPaddingAddition, the
Rekey/Reject/Keepalive timers, MaxHandshakeAttempts, RandomTrailers,
DisableCookies) are read from the conf and emitted only when non-empty, so 2.0
output stays byte-identical — verified by diffing both the client .conf and the
full vpn:// string against the previous implementation.

Changing generation invalidates every issued vpn:// key, so add
POST /api/users/reissue. It recovers the client private key from inside the
stored blob (the only place it exists), keeping ip/pub_key/psk_key intact, so
nothing changes on the wire and users only need to re-import. users gains
key_gen and vpn_key_prev, and users.db is snapshotted before the pass.

install.sh gates 3.1 on module 3.x and kernel >= 5.5 (header protection needs
the chacha library API, absent before 5.5) and falls back to writing a 2.0 conf
instead of aborting, so older kernels keep working as before.
HeaderProtectionKey is generated with awg genpsk and preserved on KEEP_DATA.

The panel marks keys issued on a different generation and offers to reissue
them; /api/v1 now returns gen alongside name/ip/vpn_key.

Also add MIT license headers across the awg-ui sources.

awg-ui/src/lib/shared.ts

@@ -1,10 +1,16 @@
+// Copyright (c) 2026 Ivan Vasilev
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
 // Общие типы, константы и утилиты для всех вкладок панели.
 import axios from 'axios';
+// Поколение протокола AmneziaWG, на параметрах которого выдан vpn:// ключ.
+export type AwgGen = '2' | '3.1';
 export interface User {
     name:          string;
     ip:            string;
     pub_key:       string;
     vpn_key:       string;
+    key_gen:       AwgGen;
     online:        boolean;
     lastHandshake: number;
     rx?:           number;
@@ -14,6 +20,7 @@ export interface ServerInfo {
     name:  string;
     ip:    string;
     peers: number;
+    gen:   AwgGen;
 }
 export interface ApiKey {
     id:         number;