fix(outbounds): support proxyProtocol on freedom outbound

Xray's freedom outbound accepts a numeric proxyProtocol (0 disabled,
1 or 2 for the PROXY protocol version), but the panel had no field for
it and the typed form adapter dropped the key on save — so a value set
via the JSON editor disappeared the moment the outbound was saved.

Model proxyProtocol through the freedom wire schema, the form schema,
and both adapter directions (clamped to 0/1/2, omitted from the wire
when 0), and add a Select (none / v1 / v2) to the freedom section of
the outbound form. Add round-trip test coverage and the proxyProtocol
label across all locales.

Closes #4486

web/translation/ru-RU.json

@@ -1209,6 +1209,7 @@
         "interface": "Интерфейс",
         "ipv6Only": "Только IPv6",
         "acceptProxyProtocol": "Принимать proxy protocol",
+        "proxyProtocol": "Proxy protocol",
         "tcpUserTimeoutMs": "TCP user timeout (мс)",
         "tcpKeepAliveIdleS": "TCP keep-alive idle (с)"
       },