refactor(rpc): Centralize RPC service and unify API (#1427)

This change introduces a major refactoring of the RPC service layer to improve modularity, unify the API, and simplify the overall architecture.

Key changes:
- Replaced per-network-instance RPC services with a single global RPC server, reducing resource usage and simplifying management.
- All clients (CLI, Web UI, etc.) now interact with EasyTier core through a unified RPC entrypoint, enabling consistent authentication and control.
- RPC implementation logic has been moved to `easytier/src/rpc_service/` and organized by functionality (e.g., `instance_manage.rs`, `peer_manage.rs`, `config.rs`) for better maintainability.
- Standardized Protobuf API definitions under `easytier/src/proto/` with an `api_` prefix (e.g., `cli.proto` → `api_instance.proto`) to provide a consistent interface.
- CLI commands now require explicit `--instance-id` or `--instance-name` when multiple network instances are running; the parameter is optional when only one instance exists.

BREAKING CHANGE:  
RPC portal configuration (`rpc_portal` and `rpc_portal_whitelist`) has been removed from per-instance configs and the Web UI. The RPC listen address must now be specified globally via the `--rpc-portal` command-line flag or the `ET_RPC_PORTAL` environment variable, as there is only one RPC service for the entire application.

easytier/src/web_client/session.rs

@@ -9,12 +9,10 @@ use tokio::{
 use crate::{
     common::{constants::EASYTIER_VERSION, get_machine_id},
     proto::{
+        api::manage::WebClientServiceServer,
         rpc_impl::bidirect::BidirectRpcManager,
         rpc_types::controller::BaseController,
-        web::{
-            HeartbeatRequest, HeartbeatResponse, WebClientServiceServer,
-            WebServerServiceClientFactory,
-        },
+        web::{HeartbeatRequest, HeartbeatResponse, WebServerServiceClientFactory},
     },
     tunnel::Tunnel,
 };
@@ -41,10 +39,10 @@ impl Session {
         let rpc_mgr = BidirectRpcManager::new();
         rpc_mgr.run_with_tunnel(tunnel);
 
-        rpc_mgr
-            .rpc_server()
-            .registry()
-            .register(WebClientServiceServer::new(controller.clone()), "");
+        rpc_mgr.rpc_server().registry().register(
+            WebClientServiceServer::new(controller.get_rpc_service()),
+            "",
+        );
 
         let mut tasks: JoinSet<()> = JoinSet::new();
         let heartbeat_ctx =