projectLead_list query is unoptimized

[trillium]

Overview

Optimize UserController.projectManager_list to reduce latency from sequential project fetches.

Action Items

• Replace per-project Project.findById calls with a single Project.find({ _id: { $in: [...] } }).
• Refactor logic to map projects to users after bulk fetch.
• Only use Promise.all if bulk fetch isn't feasible.

Resources/Instructions

• Mongoose $in operator

[JackHaeg]

Completed as part of #1977