feat(core): implement Git repository operations with gRPC services

- Add advertise_refs functionality for Git protocol communication
- Implement archive service with TAR/ZIP format support and streaming
- Create blame service for Git file annotation with line tracking
- Add branch management including create, delete, rename and compare operations
- Implement merge checking with conflict detection and fast-forward handling
- Add cherry-pick functionality for applying commits between branches
- Integrate gix library for Git repository operations and object handling
- Add comprehensive test suite covering all Git operations
- Implement proper error handling and repository validation
- Add pagination support for large result sets
- Create protobuf definitions for all Git operations and data structures
- Add build system for gRPC code generation and dependency management

proto/tag.proto

@@ -0,0 +1,67 @@
+syntax = "proto3";
+
+package gitks;
+
+import "google/protobuf/empty.proto";
+import "oid.proto";
+import "repository.proto";
+import "tagger.proto";
+
+message Tag {
+  string name = 1;
+  string full_ref = 2;
+  Oid target_oid = 3;
+  ObjectType target_type = 4;
+  Oid tag_oid = 5;
+  bool annotated = 6;
+  Signature tagger = 7;
+  string message = 8;
+  VerifiedSignature signature = 9;
+  bytes raw = 10;
+}
+
+message ListTagsRequest {
+  RepositoryHeader repository = 1;
+  string pattern = 2;
+  Pagination pagination = 3;
+  SortDirection sort_direction = 4;
+}
+
+message ListTagsResponse {
+  repeated Tag tags = 1;
+  PageInfo page_info = 2;
+}
+
+message GetTagRequest {
+  RepositoryHeader repository = 1;
+  string name = 2;
+  bool include_raw = 3;
+}
+
+message CreateTagRequest {
+  RepositoryHeader repository = 1;
+  string name = 2;
+  ObjectSelector target = 3;
+  string message = 4;
+  Signature tagger = 5;
+  bool force = 6;
+  bool annotated = 7;
+}
+
+message DeleteTagRequest {
+  RepositoryHeader repository = 1;
+  string name = 2;
+}
+
+message VerifyTagRequest {
+  RepositoryHeader repository = 1;
+  string name = 2;
+}
+
+service TagService {
+  rpc ListTags(ListTagsRequest) returns (ListTagsResponse);
+  rpc GetTag(GetTagRequest) returns (Tag);
+  rpc CreateTag(CreateTagRequest) returns (Tag);
+  rpc DeleteTag(DeleteTagRequest) returns (google.protobuf.Empty);
+  rpc VerifyTag(VerifyTagRequest) returns (VerifiedSignature);
+}