feat(service): expand service layer with new domain operations

- Add IM service modules: audit, channel roles, custom emojis, forum
  tags, integrations, invitations, repo links, slash commands, stages,
  voice, webhooks
- Add PR service modules: review requests, templates
- Add repo service modules: contributors, release assets, git extras
  (archive, branch rename, commit extras, diff/merge, tag, tree)
- Add user service: social (follow/block)
- Add internal auth service
- Update existing service modules with expanded functionality
- Remove deleted IM modules: articles, delivery trace, drafts,
  follows, messages, polls, presence, reactions, threads

service/repo/git/repository.rs

@@ -120,4 +120,29 @@ impl RepoService {
             .map_err(|e| AppError::InternalServerError(e.to_string()))?;
         Ok(resp.into_inner())
     }
+
+    pub async fn git_set_default_branch(
+        &self,
+        ctx: &Session,
+        wk_name: &str,
+        repo_name: &str,
+        branch_name: &str,
+    ) -> Result<(), AppError> {
+        let user_uid = ctx.user().ok_or(AppError::Unauthorized)?;
+        let repo = self.resolve_repo(wk_name, repo_name).await?;
+        self.ensure_repo_role_at_least(user_uid, &repo, crate::models::common::Role::Admin)
+            .await?;
+        let ws = self.resolve_workspace(wk_name).await?;
+        let header = self.repo_header(&repo, &ws);
+        let mut svc = self.git_client(&repo)?.repository;
+        svc.set_default_branch(tonic::Request::new(
+            crate::pb::repo::SetDefaultBranchRequest {
+                repository: Some(header),
+                name: branch_name.to_string(),
+            },
+        ))
+        .await
+        .map_err(|e| AppError::InternalServerError(e.to_string()))?;
+        Ok(())
+    }
 }