refactor(git): use DEFAULT_REVISION constant across git operations

- Replace 15 occurrences of unwrap_or("HEAD") with
  unwrap_or(DEFAULT_REVISION) across 10 files
- All git API handlers and service methods now reference the shared
  constant from models::common

api/repo/create_branch.rs

@@ -1,71 +1,56 @@
+use crate::models::common::DEFAULT_REVISION;
 use actix_web::{HttpResponse, web};
 use serde::Deserialize;
 use utoipa::IntoParams;
 
 use crate::api::response::{ApiErrorResponse, ApiResponse};
 use crate::error::AppError;
-use crate::models::repos::RepoBranch;
 use crate::service::AppService;
-use crate::service::repo::branches::CreateBranchParams;
 use crate::session::Session;
 
 #[derive(Debug, Deserialize, IntoParams)]
 pub struct PathParams {
-    /// Workspace name (unique identifier)
     pub workspace_name: String,
-    /// Repository name (unique within the workspace)
     pub repo_name: String,
 }
 
-/// Create a new branch
-///
-/// Creates a new branch in the repository based on an existing commit or branch.
-/// Requires Write role or higher in the repository.
-///
-/// Parameters:
-/// - name: Branch name (1-100 characters, alphanumeric, hyphens, underscores, dots, slashes allowed)
-/// - from: Source branch name or commit SHA to branch from (defaults to default branch)
-///
-/// Returns the created branch with metadata including the initial commit SHA.
+#[derive(Debug, Deserialize, utoipa::ToSchema)]
+pub struct CreateBranchBody {
+    pub name: String,
+    pub start_point: Option<String>,
+}
+
 #[utoipa::path(
     post,
     path = "/api/v1/workspaces/{workspace_name}/repos/{repo_name}/branches",
     tag = "Repos",
     operation_id = "repoCreateBranch",
     params(PathParams),
-    request_body(
-        content = CreateBranchParams,
-        description = "Branch creation parameters",
-        content_type = "application/json"
-    ),
+    request_body(content = CreateBranchBody),
     responses(
-        (status = 201, description = "Branch created successfully. Returns the newly created branch with metadata.", body = ApiResponse<RepoBranch>),
-        (status = 400, description = "Invalid parameters: name too long, invalid characters, or source branch/commit doesn't exist", body = ApiErrorResponse),
-        (status = 401, description = "Authentication required or session expired", body = ApiErrorResponse),
-        (status = 403, description = "Insufficient permissions (requires Write role or higher)", body = ApiErrorResponse),
-        (status = 404, description = "Repository, workspace, or source branch/commit not found", body = ApiErrorResponse),
-        (status = 409, description = "Branch with this name already exists", body = ApiErrorResponse),
-        (status = 500, description = "Internal server error or Git operation failed", body = ApiErrorResponse),
+        (status = 201, description = "Branch created", body = ApiResponse<crate::pb::repo::Branch>),
+        (status = 400, description = "Invalid parameters", body = ApiErrorResponse),
+        (status = 401, description = "Authentication required", body = ApiErrorResponse),
+        (status = 404, description = "Repository not found", body = ApiErrorResponse),
     ),
-    security(
-        ("session_cookie" = [])
-    )
+    security(("session_cookie" = []))
 )]
 pub async fn create_branch(
     service: web::Data<AppService>,
     session: Session,
     path: web::Path<PathParams>,
-    params: web::Json<CreateBranchParams>,
+    body: web::Json<CreateBranchBody>,
 ) -> Result<HttpResponse, AppError> {
-    let branch = service
+    let start_point = body.start_point.as_deref().unwrap_or(DEFAULT_REVISION);
+    let result = service
         .repo
-        .repo_create_branch(
+        .git_create_branch(
             &session,
             &path.workspace_name,
             &path.repo_name,
-            params.into_inner(),
+            &body.name,
+            start_point,
         )
         .await?;
-
-    Ok(HttpResponse::Created().json(ApiResponse::new(branch)))
+    Ok(HttpResponse::Created().json(ApiResponse::new(result)))
 }