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/schemas/forms/outbound-form.ts

@@ -166,6 +166,7 @@ export type FreedomFinalRuleForm = z.infer<typeof FreedomFinalRuleFormSchema>;
 export const FreedomOutboundFormSettingsSchema = z.object({
   domainStrategy: z.union([OutboundDomainStrategySchema, z.literal('')]).default(''),
   redirect: z.string().default(''),
+  proxyProtocol: z.number().int().min(0).max(2).default(0),
   fragment: FreedomFragmentSchema.default({
     packets: '1-3',
     length: '',