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

frontend/src/lib/xray/outbound-form-adapter.ts

@@ -265,6 +265,10 @@ function freedomFromWire(raw: Raw): FreedomOutboundFormSettings {
       return (allowed.includes(s) ? s : '') as FreedomOutboundFormSettings['domainStrategy'];
     })(),
     redirect: asString(raw.redirect),
+    proxyProtocol: ((): FreedomOutboundFormSettings['proxyProtocol'] => {
+      const n = asNumber(raw.proxyProtocol, 0);
+      return (n === 1 || n === 2) ? n : 0;
+    })(),
     fragment: wireHasFragment
       ? {
           packets: asString(fragment.packets, '1-3'),
@@ -489,6 +493,7 @@ function freedomToWire(s: FreedomOutboundFormSettings) {
   return {
     domainStrategy: s.domainStrategy || undefined,
     redirect: s.redirect || undefined,
+    proxyProtocol: s.proxyProtocol || undefined,
     fragment: fragmentEnabled ? Object.fromEntries(fragmentEntries) : undefined,
     noises: s.noises.length > 0 ? s.noises : undefined,
     finalRules: s.finalRules.length > 0