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>

proto/mc_proxy/v1/admin.proto

@@ -26,6 +26,11 @@ service ProxyAdminService {
 message Route {
   string hostname = 1;
   string backend = 2;
+  string mode = 3;                // "l4" (default) or "l7"
+  string tls_cert = 4;            // PEM certificate path (L7 only)
+  string tls_key = 5;             // PEM private key path (L7 only)
+  bool backend_tls = 6;           // re-encrypt to backend (L7 only)
+  bool send_proxy_protocol = 7;   // send PROXY v2 header to backend
 }
 
 message ListRoutesRequest {
@@ -89,6 +94,7 @@ message ListenerStatus {
   string addr = 1;
   int32 route_count = 2;
   int64 active_connections = 3;
+  bool proxy_protocol = 4;
 }
 
 message GetStatusRequest {}