Eliminate Duplicate Snapshot Creation Code

[gzark1]

Description

Snapshot creation logic is duplicated in two places, violating DRY and the repository pattern. Both locations use direct db.add() instead of a repository method.

Steps to Reproduce

1. Open backend/core/user_manager.py:64-74
2. Open backend/services/profile_service.py:70-79
3. Compare the snapshot creation code - nearly identical

Expected Behavior

Snapshot creation should be a single method in UserProfileRepository:
await repo.create_snapshot(profile)

Actual Behavior

Two separate locations create snapshots with duplicated code:

Location 1: core/user_manager.py:64-74 (registration)

• Creates UserProfileSnapshot with hardcoded version=1
• Uses db.add(snapshot) directly

Location 2: services/profile_service.py:70-79 (profile update)

• Creates UserProfileSnapshot with updated_profile.version
• Uses self.db.add(snapshot) directly

Root Cause

• Service layer (profile_service.py) bypasses repository for snapshot creation
• user_manager.py has no access to repositories (fastapi-users hook limitation)
• No create_snapshot() method exists in UserProfileRepository

Possible Solutions

1. Option A: Add create_snapshot() to UserProfileRepository

   • Add method to repositories/user_profile_repository.py
   • Update profile_service.py to use self.repo.create_snapshot()
   • Update user_manager.py to instantiate repo and use it

2. Option B: Create standalone snapshot utility

   • Create utils/snapshot.py with create_snapshot(db, profile) function
   • Both locations import and use the utility
   • Less pure but simpler given fastapi-users constraints