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- Remove immediate/ real-time module (superseded by IM service)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

proto/git/diff.proto

@@ -132,9 +132,67 @@ message GetDiffStatsRequest {
   DiffOptions options = 4;
 }
 
+
+message RawDiffRequest {
+  RepositoryHeader repository = 1;
+  string base = 2;       // revision or OID
+  string head = 3;
+  DiffOptions options = 4;
+}
+
+message RawDiffResponse {
+  bytes data = 1;
+}
+
+message RawPatchRequest {
+  RepositoryHeader repository = 1;
+  string base = 2;
+  string head = 3;
+}
+
+message RawPatchResponse {
+  bytes data = 1;
+}
+
+
+message FindChangedPathsRequest {
+  RepositoryHeader repository = 1;
+  string base = 2;
+  string head = 3;
+  repeated string paths = 4; // filter to these paths
+}
+
+message ChangedPath {
+  enum Status {
+    CHANGED_PATH_STATUS_UNSPECIFIED = 0;
+    CHANGED_PATH_STATUS_ADDED = 1;
+    CHANGED_PATH_STATUS_MODIFIED = 2;
+    CHANGED_PATH_STATUS_DELETED = 3;
+    CHANGED_PATH_STATUS_RENAMED = 4;
+    CHANGED_PATH_STATUS_COPIED = 5;
+    CHANGED_PATH_STATUS_TYPE_CHANGED = 6;
+  }
+
+  Status status = 1;
+  string old_path = 2;
+  string new_path = 3;
+  uint32 additions = 4;
+  uint32 deletions = 5;
+  bool binary = 6;
+}
+
+message FindChangedPathsResponse {
+  repeated ChangedPath paths = 1;
+}
+
 service DiffService {
   rpc GetDiff(GetDiffRequest) returns (GetDiffResponse);
   rpc GetCommitDiff(GetCommitDiffRequest) returns (GetDiffResponse);
   rpc GetPatch(GetPatchRequest) returns (stream GetPatchResponse);
   rpc GetDiffStats(GetDiffStatsRequest) returns (DiffStats);
+
+  rpc RawDiff(RawDiffRequest) returns (stream RawDiffResponse);
+  rpc RawPatch(RawPatchRequest) returns (stream RawPatchResponse);
+
+  rpc FindChangedPaths(FindChangedPathsRequest) returns (FindChangedPathsResponse);
 }