feat(mtproto): add domain-fronting and essential mtg options

Expose mtg's [domain-fronting] section (ip/port/proxy-protocol) plus
proxy-protocol-listener, prefer-ip, and debug on MTProto inbounds. Each
key is written to the generated mtg-<id>.toml only when set, so mtg's own
defaults apply otherwise. The instance fingerprint now covers these
fields, so editing an option restarts the sidecar.

Since MTProto is mtg-served (not Xray), sniffing does not apply: hide the
Sniffing tab and the Advanced sniffing sub-editor, drop it from the
Advanced "All" JSON view, and emit empty sniffing in the wire payload,
all gated by a new canEnableSniffing predicate.

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

@@ -11,6 +11,7 @@ import type { StreamSettings } from '@/schemas/api/inbound';
 import type { Sniffing } from '@/schemas/primitives';
 import type { z } from 'zod';
 import { normalizeStreamSettingsForWire } from '@/lib/xray/stream-wire-normalize';
+import { canEnableSniffing } from '@/lib/xray/protocol-capabilities';
 
 // Plain-data adapter between the panel's stored inbound row shape and
 // the typed InboundFormValues that Form.useForm<T> carries inside
@@ -302,7 +303,9 @@ export function formValuesToWirePayload(values: InboundFormValues): WireInboundP
     protocol: values.protocol,
     settings: JSON.stringify(settingsPruned),
     streamSettings: streamPruned ? JSON.stringify(streamPruned) : '',
-    sniffing: JSON.stringify(normalizeSniffing(values.sniffing)),
+    // mtproto is mtg-served, not Xray, so sniffing never applies — emit empty
+    // rather than the default { enabled: false } so the row carries no sniffing.
+    sniffing: canEnableSniffing({ protocol: values.protocol }) ? JSON.stringify(normalizeSniffing(values.sniffing)) : '',
     tag: values.tag,
   };
   if (values.nodeId != null) payload.nodeId = values.nodeId;

frontend/src/lib/xray/protocol-capabilities.ts

@@ -50,6 +50,12 @@ export function canEnableStream(values: { protocol: string }): boolean {
   return STREAM_PROTOCOLS.includes(values.protocol);
 }
 
+// mtproto is served by an external mtg process, not Xray, so the Xray sniffing
+// block does not apply to it. Every other inbound supports sniffing.
+export function canEnableSniffing(values: { protocol: string }): boolean {
+  return values.protocol !== 'mtproto';
+}
+
 // Vision seed applies only when XTLS Vision (TCP/TLS) flow is selected
 // AND at least one VLESS client uses the vision flow. Excludes UDP variant.
 export function canEnableVisionSeed(values: CapabilityVlessSlice): boolean {