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/peers/peer_ospf_route.rs

@@ -193,7 +193,7 @@ impl RoutePeerInfo {
     }
 }
 
-impl From<RoutePeerInfo> for crate::proto::cli::Route {
+impl From<RoutePeerInfo> for crate::proto::api::instance::Route {
     fn from(val: RoutePeerInfo) -> Self {
         let network_length = if val.network_length == 0 {
             24
@@ -201,7 +201,7 @@ impl From<RoutePeerInfo> for crate::proto::cli::Route {
             val.network_length
         };
 
-        crate::proto::cli::Route {
+        crate::proto::api::instance::Route {
             peer_id: val.peer_id,
             ipv4_addr: val.ipv4_addr.map(|ipv4_addr| Ipv4Inet {
                 address: Some(ipv4_addr),
@@ -2361,7 +2361,7 @@ impl Route for PeerRoute {
             .map(|x| x.next_hop_peer_id)
     }
 
-    async fn list_routes(&self) -> Vec<crate::proto::cli::Route> {
+    async fn list_routes(&self) -> Vec<crate::proto::api::instance::Route> {
         let route_table = &self.service_impl.route_table;
         let route_table_with_cost = &self.service_impl.route_table_with_cost;
         let mut routes = Vec::new();
@@ -2373,7 +2373,7 @@ impl Route for PeerRoute {
                 continue;
             };
             let next_hop_peer_latency_first = route_table_with_cost.get_next_hop(*item.key());
-            let mut route: crate::proto::cli::Route = item.value().clone().into();
+            let mut route: crate::proto::api::instance::Route = item.value().clone().into();
             route.next_hop_peer_id = next_hop_peer.next_hop_peer_id;
             route.cost = next_hop_peer.path_len as i32;
             route.path_latency = next_hop_peer.path_latency;