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

branch/get_branch.rs

@@ -0,0 +1,23 @@
+use crate::bare::GitBare;
+use crate::error::GitResult;
+use crate::pb::{Branch, GetBranchRequest};
+
+impl GitBare {
+    pub fn get_branch(&self, request: GetBranchRequest) -> GitResult<Branch> {
+        let repo = self.gix_repo()?;
+        let refname = format!("refs/heads/{}", request.name);
+        let mut r = repo.find_reference(refname.as_str())?;
+        let hex = r.peel_to_id()?.to_string();
+        Ok(Branch {
+            name: request.name,
+            full_ref: refname,
+            target_oid: Some(self.oid_to_pb(hex)),
+            commit: None,
+            upstream: None,
+            is_default: false,
+            is_head: false,
+            is_merged: false,
+            is_detached: false,
+        })
+    }
+}