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/proto/api_config.proto

@@ -0,0 +1,74 @@
+syntax = "proto3";
+
+import "common.proto";
+import "acl.proto";
+import "api_instance.proto";
+
+package api.config;
+
+enum ConfigPatchAction {
+  ADD = 0;
+  REMOVE = 1;
+  CLEAR = 2;
+}
+
+message InstanceConfigPatch {
+  optional string hostname = 1;
+  optional common.Ipv4Inet ipv4 = 2;
+  optional common.Ipv6Inet ipv6 = 3;
+  repeated PortForwardPatch port_forwards = 4;
+  optional AclPatch acl = 5;
+  repeated ProxyNetworkPatch proxy_networks = 6;
+  repeated RoutePatch routes = 7;
+  repeated ExitNodePatch exit_nodes = 8;
+  repeated UrlPatch mapped_listeners = 9;
+  repeated UrlPatch connectors = 10;
+}
+
+message PortForwardPatch {
+  ConfigPatchAction action = 1;
+  common.PortForwardConfigPb cfg = 2;
+}
+
+message StringPatch {
+  ConfigPatchAction action = 1;
+  string value = 2;
+}
+
+message UrlPatch {
+  ConfigPatchAction action = 1;
+  common.Url url = 2;
+}
+
+message AclPatch {
+  optional acl.Acl acl = 1;
+  repeated StringPatch tcp_whitelist = 2;
+  repeated StringPatch udp_whitelist = 3;
+}
+
+message ProxyNetworkPatch {
+  ConfigPatchAction action = 1;
+  common.Ipv4Inet cidr = 2;
+  optional common.Ipv4Inet mapped_cidr = 3;
+}
+
+message RoutePatch {
+  ConfigPatchAction action = 1;
+  common.Ipv4Inet cidr = 2;
+}
+
+message ExitNodePatch {
+  ConfigPatchAction action = 1;
+  common.IpAddr node = 2;
+}
+
+message PatchConfigRequest {
+  InstanceConfigPatch patch = 1;
+  api.instance.InstanceIdentifier instance = 2;
+}
+
+message PatchConfigResponse {}
+
+service ConfigRpc {
+  rpc PatchConfig(PatchConfigRequest) returns (PatchConfigResponse);
+}