Add L7 and PROXY protocol fields to gRPC API and CLI

Proto: Route message gains mode, tls_cert, tls_key, backend_tls,
send_proxy_protocol fields. ListenerStatus gains proxy_protocol.
Generated code regenerated with protoc v29.5.

gRPC server: AddRoute validates mode ("l4"/"l7", defaults to "l4"),
requires tls_cert/tls_key for L7 routes, persists all fields via
write-through. ListRoutes returns full route info. GetStatus
includes proxy_protocol on listener status.

Client package: Route struct expanded with Mode, TLSCert, TLSKey,
BackendTLS, SendProxyProtocol. AddRoute signature changed to accept
a Route struct instead of individual hostname/backend strings.
ListenerStatus gains ProxyProtocol. ListRoutes maps all proto fields.

mcproxyctl: routes add gains --mode, --tls-cert, --tls-key,
--backend-tls, --send-proxy-protocol flags. routes list displays
mode and option tags for each route.

New tests: add L7 route via gRPC with field round-trip verification,
L7 route missing cert/key (InvalidArgument), invalid mode rejection,
default-to-L4 backward compatibility, proxy_protocol in status.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gen/mc_proxy/v1/admin_grpc.pb.go

@@ -1,7 +1,7 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
 // - protoc-gen-go-grpc v1.6.1
-// - protoc             v6.33.4
+// - protoc             v5.29.5
 // source: proto/mc_proxy/v1/admin.proto
 
 package mcproxyv1