Bud Foundry model list is global, not per-user — last sync overwrites for everyone

[dittops]

Problem

The ModelConfiguration table has no user_id column — it stores model configurations globally. When a user's Bud Foundry models are synced via update_bud_foundry_model_configurations() in backend/onyx/db/llm.py, it performs a DELETE ALL + INSERT with the current user's available models. This means the last user to trigger a sync overwrites the model list for everyone.

Reproduction

1. User A logs in with OAuth — has access to 3 Bud Foundry models
2. _sync_bud_foundry_models_to_db() runs → DB now has 3 ModelConfiguration rows
3. User B logs in — has access to 0 Bud Foundry models (or different ones)
4. _sync_bud_foundry_models_to_db() runs → DB now has 0 rows (User A's models deleted)
5. User A's agent tries to use a model → falls back to default list or fails

Observed Behavior

• When a user has no Bud Foundry models available, they see the full model list from another user who synced previously
• Error message: "No models available from Bud Foundry for this user" triggers fallback to stale global list

Root Cause

• ModelConfiguration table lacks a user_id foreign key
• update_bud_foundry_model_configurations() (backend/onyx/db/llm.py ~line 350) deletes ALL rows then inserts current user's models
• _sync_bud_foundry_models_to_db() (backend/onyx/llm/factory.py ~line 106) calls the above without user scoping

Proposed Fix

1. Add user_id FK column to ModelConfiguration (alembic migration)
2. Scope update_bud_foundry_model_configurations() to delete/insert only for the current user
3. Scope model queries in _resolve_bud_foundry_model() to filter by user_id
4. Update get_default_llms() to pass user context through the model resolution chain

Key Files

• backend/onyx/db/llm.py — update_bud_foundry_model_configurations()
• backend/onyx/llm/factory.py — _sync_bud_foundry_models_to_db(), _resolve_bud_foundry_model(), get_default_llms()
• backend/onyx/db/models.py — ModelConfiguration model