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/peer_center/instance.rs

@@ -39,7 +39,7 @@ pub trait PeerCenterPeerManagerTrait: Send + Sync + 'static {
     fn my_peer_id(&self) -> PeerId;
     fn get_global_ctx(&self) -> Arc<GlobalCtx>;
     fn get_rpc_mgr(&self) -> Weak<PeerRpcManager>;
-    async fn list_routes(&self) -> Vec<crate::proto::cli::Route>;
+    async fn list_routes(&self) -> Vec<crate::proto::api::instance::Route>;
 }
 
 struct PeerCenterBase {
@@ -426,7 +426,7 @@ impl PeerCenterPeerManagerTrait for PeerManager {
         Arc::downgrade(&self.get_peer_rpc_mgr())
     }
 
-    async fn list_routes(&self) -> Vec<crate::proto::cli::Route> {
+    async fn list_routes(&self) -> Vec<crate::proto::api::instance::Route> {
         self.list_routes().await
     }
 }
@@ -478,7 +478,7 @@ impl PeerCenterPeerManagerTrait for PeerMapWithPeerRpcManager {
         Arc::downgrade(&self.rpc_mgr)
     }
 
-    async fn list_routes(&self) -> Vec<crate::proto::cli::Route> {
+    async fn list_routes(&self) -> Vec<crate::proto::api::instance::Route> {
         self.peer_map.list_route_infos().await
     }
 }