refactor(slm): consolidate User models to single UUID-PK (#1900)

[mrveiss]

Summary

• Consolidate two conflicting SLM User models (integer PK vs UUID PK) into a single UUID-PK model
• Remove legacy User class from models/database.py (was slm_users table)
• Update all auth services to use the user_management.models.user.User model
• Add data migration to move legacy slm_users rows into UUID users table

Files Changed

File	Change
models/database.py	Removed User class (19 lines)
services/auth.py	Import from user_management.models.user; is_admin → is_platform_admin, last_login → last_login_at
main.py	_ensure_admin_user() rewritten to use UserService + get_slm_session()
api/auth.py	DB session switched from get_db to get_slm_db for user operations
models/schemas.py	UserResponse.id accepts UUID; added model_validate override for field mapping
migrations/consolidate_slm_users_to_uuid.py	New — migrates slm_users rows to UUID users table, drops slm_users
migrations/runner.py	Added migration to runner list

Consolidated User Model (UUID PK)

Single source: user_management/models/user.py with fields: id (UUID), email, username, password_hash, display_name, is_active, is_verified, mfa_enabled, is_platform_admin, preferences (JSONB), last_login_at, created_at, updated_at, deleted_at

Migration Strategy

1. rename_users_to_slm_users (existing) — renames integer-PK users → slm_users
2. consolidate_slm_users_to_uuid (new) — reads slm_users rows, inserts into UUID users table, drops slm_users

Safe to re-run. Fresh installs skip automatically (no slm_users table exists).

Notes

• Docker workaround (separate slm_users database) remains as correct architecture — not a workaround
• Two login endpoints coexist (/api/auth/login + /api/slm-auth/login) — dedup is a separate task
• Frontend consuming POST /api/auth/users should be checked for integer-id assumptions (now returns UUID strings)

Test plan

• SLM starts cleanly with no existing slm_users table (fresh install)
• Migration runs correctly on existing data (moves rows, drops table)
• Admin user creation works via _ensure_admin_user()
• Login via /api/auth/login works with consolidated model
• UserResponse serializes UUID id correctly

Closes #1900