feat(amneziawg): add native AmneziaWG protocol backend

AmneziaWG (WireGuard plus DPI-resistant obfuscation) needs no Docker
here — it runs as a genuine kernel interface via awg-quick/awg, managed
the same way internal/mtproto manages mtg: one Inbound row is one
desired Instance, and a Manager reconciles running interfaces toward
the database every 10s (internal/web/job/amneziawg_job.go) plus
immediately after a client edit (applyLocalAmneziaWG).

Clients reuse model.Client verbatim (the same PrivateKey/PublicKey/
PreSharedKey/AllowedIPs fields WireGuard already uses), so bulk
operations, the QR/share-link modal and subscriptions come from the
shared inbound infrastructure instead of a parallel implementation.
internal/amneziawg owns the obfuscation param generator/validator
(ported from coinman-dev/3ax-ui, upgraded to AmneziaWG 2.0's S3/S4
padding and I1 signature packet) and the exec wrapper around
awg-quick/awg, with fingerprint-based reconcile (noop / reload-via-
syncconf / full restart) mirroring mtproto.Manager so a same-protocol
edit doesn't force an unnecessary interface bounce that would drop
every peer's connection.

Frontend and install.sh's DKMS/awg-tools setup are tracked separately;
this is backend-only.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/web/service/xray.go

@@ -139,7 +139,7 @@ func (s *XrayService) GetXrayConfig() (*xray.Config, error) {
 		if inbound.NodeID != nil {
 			continue
 		}
-		if inbound.Protocol == model.MTProto {
+		if inbound.Protocol == model.MTProto || inbound.Protocol == model.AmneziaWG {
 			continue
 		}
 		settings := map[string]any{}