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/compare_branch.rs

@@ -0,0 +1,54 @@
+use crate::bare::GitBare;
+use crate::error::{GitError, GitResult};
+use crate::pb::{CompareBranchRequest, CompareBranchResponse};
+
+impl GitBare {
+    pub fn compare_branch(
+        &self,
+        request: CompareBranchRequest,
+    ) -> GitResult<CompareBranchResponse> {
+        let repo = self.gix_repo()?;
+        let source_ref = format!("refs/heads/{}", request.source_branch);
+        let target_ref = format!("refs/heads/{}", request.target_branch);
+        let source_id = repo.find_reference(source_ref.as_str())?.peel_to_id()?;
+        let target_id = repo.find_reference(target_ref.as_str())?.peel_to_id()?;
+        let source_hex = source_id.to_string();
+        let target_hex = target_id.to_string();
+        let merge_base = repo
+            .merge_base(source_id.detach(), target_id.detach())
+            .ok()
+            .map(|id| self.oid_to_pb(id.to_string()));
+        let result = duct::cmd(
+            "git",
+            [
+                "--git-dir",
+                self.bare_dir.to_string_lossy().as_ref(),
+                "rev-list",
+                "--left-right",
+                "--count",
+                &format!("{}...{}", source_hex, target_hex),
+            ],
+        )
+        .stdout_capture()
+        .stderr_capture()
+        .unchecked()
+        .run()?;
+        if !result.status.success() {
+            return Err(GitError::CommandFailed {
+                status_code: result.status.code(),
+                stderr: String::from_utf8_lossy(&result.stderr).into_owned(),
+            });
+        }
+        let output = String::from_utf8_lossy(&result.stdout);
+        let parts: Vec<&str> = output.split_whitespace().collect();
+        let ahead_by = parts.first().and_then(|s| s.parse().ok()).unwrap_or(0);
+        let behind_by = parts.get(1).and_then(|s| s.parse().ok()).unwrap_or(0);
+        Ok(CompareBranchResponse {
+            ahead: ahead_by > 0,
+            behind: behind_by > 0,
+            ahead_by,
+            behind_by,
+            merge_base,
+        })
+    }
+}