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/issues/milestones.rs

@@ -126,12 +126,34 @@ impl IssueService {
         let repo_id = self.resolve_repo_id(wk_name, repo_name).await?;
         self.ensure_repo_role(repo_id, user_uid, Role::Admin)
             .await?;
+
+        let mut txn = self
+            .ctx
+            .db
+            .writer()
+            .begin()
+            .await
+            .map_err(|_| AppError::TxnError)?;
+
+        // Clear milestone_id from all issues that reference this milestone
+        sqlx::query(
+            "UPDATE issue SET milestone_id = NULL, updated_at = $1 WHERE milestone_id = $2",
+        )
+        .bind(chrono::Utc::now())
+        .bind(milestone_id)
+        .execute(&mut *txn)
+        .await
+        .map_err(AppError::Database)?;
+
         let result = sqlx::query("DELETE FROM issue_milestone WHERE id = $1 AND repo_id = $2")
             .bind(milestone_id)
             .bind(repo_id)
-            .execute(self.ctx.db.writer())
+            .execute(&mut *txn)
             .await
             .map_err(AppError::Database)?;
-        ensure_affected(result.rows_affected(), "milestone not found")
+        ensure_affected(result.rows_affected(), "milestone not found")?;
+
+        txn.commit().await.map_err(|_| AppError::TxnError)?;
+        Ok(())
     }
 }