feat(amneziawg): support persistent keepalive ranges (#6881)

AmneziaWG clients accept a randomised PersistentKeepalive range such as 15-25,
which makes keepalive timing harder to fingerprint; the panel only stored a
single number. A client's keepalive may now be a range, validated the way
AmneziaWG parses it. The downloadable .conf and vpn:// profile carry the range,
Clash/Mihomo output gets its lower bound, and plain WireGuard stays scalar-only.
The range lives in an additive wg_keep_alive_range column, so the integer
column and an older panel binary keep working after a rollback.

tools/openapigen/main.go

@@ -48,7 +48,11 @@ func run(root, outDir string) error {
 					{Field: "StreamSettings", Kind: KindAny},
 					{Field: "Sniffing", Kind: KindAny},
 				},
+				"Client": {
+					{Field: "KeepAlive", Type: TypeRef{Kind: KindUnion, Variants: []TypeRef{{Kind: KindInt}, {Kind: KindString}}}},
+				},
 				"ClientRecord": {
+					{Field: "KeepAlive", Type: TypeRef{Kind: KindUnion, Variants: []TypeRef{{Kind: KindInt}, {Kind: KindString}}}},
 					{Field: "Reverse", Kind: KindAny},
 				},
 				"InboundClientIps": {