feat(inbounds): expose Vision testseed field with sensible default

Add a "Vision testseed" form item to the inbound modal for TCP + TLS/reality
inbounds, normalized to positive integers and defaulting to [900,500,900,256].
Apply the same default in the outbound form adapter when no valid saved seed
is present.

Replace the http/mixed snapshot assertions in inbound-defaults with explicit
field checks so generated credentials don't break the snapshots.

frontend/src/test/__snapshots__/inbound-defaults.test.ts.snap

@@ -1,12 +1,5 @@
 // Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
 
-exports[`createDefault*InboundSettings factories > http 1`] = `
-{
-  "accounts": [],
-  "allowTransparent": false,
-}
-`;
-
 exports[`createDefault*InboundSettings factories > hysteria (v1, defaults to v2 wire version) 1`] = `
 {
   "clients": [],
@@ -14,15 +7,6 @@ exports[`createDefault*InboundSettings factories > hysteria (v1, defaults to v2
 }
 `;
 
-exports[`createDefault*InboundSettings factories > mixed 1`] = `
-{
-  "accounts": [],
-  "auth": "password",
-  "ip": "127.0.0.1",
-  "udp": false,
-}
-`;
-
 exports[`createDefault*InboundSettings factories > shadowsocks 1`] = `
 {
   "clients": [],