Fix missing Mongoose ref options on schema fields

[trillium]

Problem

9 fields across 6 model files are defined as plain String or Number types without a ref option, which breaks .populate() calls at runtime.

Affected Files

File	Field(s)	Current Type	Should Reference
projectTeamMember.model.js	usersId, projectId	String	User, Project
checkIn.model.js	eventId, userId	String	RecurringEvent, User
event.model.js	projectId	String	Project
recurringEvent.model.js	projectId	String	Project
user.model.js	currentRole	Number	N/A (convert to ObjectId ref to future Role model, or keep as enum — needs decision)
project.model.js	projectStatus, googleDriveId	String	N/A (convert to proper schema options)

Impact

• .populate() silently returns null for these fields because Mongoose cannot resolve the reference
• This is a prerequisite for the manager toggle feature (EPIC: As a manager, I want a Toggle Feature so that I can Enable Manager Access #2149)
• Relates to ProjectTeamMember schema is the right join table but is bypassed by redundant fields on User and Project #2155

Fix

Convert plain String fields to { type: Schema.Types.ObjectId, ref: "ModelName" } where an association exists. For fields that are true scalars (enums, IDs from external systems), ensure proper schema options are applied.

Scope

Schema-only change — no API or UI modifications required.