chore(infra): add gRPC layer, update protobufs, remove immediate module

- Add gRPC service modules: auth, channel, channel settings, member,
  permission
- Update protobuf definitions and generated code
- Remove immediate/ real-time module (superseded by IM service)
- Update etcd discovery and registration
- Update cache, error, config, and build infrastructure
- Add ADR documentation
- Update OpenAPI spec

pb/mod.rs

@@ -1,8 +1,37 @@
+pub mod appks;
 pub mod email;
+pub mod im;
 pub mod repo;
 
+use serde::{Deserialize, Serialize};
 use tonic::transport::{Channel, Endpoint};
 
+#[derive(Clone, PartialEq, Eq, Hash, prost::Message, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct Timestamp {
+    #[prost(int64, tag = "1")]
+    pub seconds: i64,
+    #[prost(int32, tag = "2")]
+    pub nanos: i32,
+}
+
+impl From<prost_types::Timestamp> for Timestamp {
+    fn from(t: prost_types::Timestamp) -> Self {
+        Self {
+            seconds: t.seconds,
+            nanos: t.nanos,
+        }
+    }
+}
+
+impl From<Timestamp> for prost_types::Timestamp {
+    fn from(t: Timestamp) -> Self {
+        Self {
+            seconds: t.seconds,
+            nanos: t.nanos,
+        }
+    }
+}
+
 #[derive(Clone)]
 pub struct RepoClient {
     pub repository: repo::repository_service_client::RepositoryServiceClient<Channel>,
@@ -15,6 +44,8 @@ pub struct RepoClient {
     pub blame: repo::blame_service_client::BlameServiceClient<Channel>,
     pub archive: repo::archive_service_client::ArchiveServiceClient<Channel>,
     pub pack: repo::pack_service_client::PackServiceClient<Channel>,
+    pub ref_: repo::ref_service_client::RefServiceClient<Channel>,
+    pub remote: repo::remote_service_client::RemoteServiceClient<Channel>,
 }
 
 impl RepoClient {
@@ -41,7 +72,9 @@ impl RepoClient {
             merge: repo::merge_service_client::MergeServiceClient::new(channel.clone()),
             blame: repo::blame_service_client::BlameServiceClient::new(channel.clone()),
             archive: repo::archive_service_client::ArchiveServiceClient::new(channel.clone()),
-            pack: repo::pack_service_client::PackServiceClient::new(channel),
+            pack: repo::pack_service_client::PackServiceClient::new(channel.clone()),
+            ref_: repo::ref_service_client::RefServiceClient::new(channel.clone()),
+            remote: repo::remote_service_client::RemoteServiceClient::new(channel),
         }
     }
 }
@@ -82,3 +115,18 @@ impl std::ops::DerefMut for EmailClient {
         &mut self.inner
     }
 }
+
+// Section: Appks gRPC server traits
+//
+// Core services (package appks.v1) live in pb::appks::
+//   - RepoService
+//
+// IM services (package appks.im.v1) live in pb::im::
+//   - ChannelService, MemberService, PermissionService
+//   - InternalAuthService
+//   - ChannelRoleService, ChannelInvitationService, ChannelWebhookService
+//   - ChannelSlashCommandService, ChannelRepoLinkService, ImIntegrationService
+//   - CustomEmojiService, ForumTagService, VoiceService, StageService
+//   - ChannelAuditService
+//
+// Implementations are in grpc/ and wired into the tonic server in grpc/mod.rs.