## Bug Description

When using `max_end_user_budget_id` in the proxy config to set a default budget for end users, the budget is only applied **in-memory** at auth time but never written to the `LiteLLM_EndUserTable` database record. This causes the budget reset job to skip these users entirely — their spend accumulates forever and never resets.

## Root Cause

Three code paths are involved:

1. **Auth-time budget application** (`auth_checks.py` → `_apply_default_budget_to_end_user()`): When a request arrives with an end-user ID, this function merges the default budget onto the in-memory `LiteLLM_EndUserTable` object by setting `end_user_obj.litellm_budget_table`. The `budget_id` column is **never written to the DB**.

2. **End user auto-creation** (`utils.py` → `update_end_user_spend()`): The upsert `create` clause only sets `user_id`, `spend`, and `blocked`. It does **not** include `budget_id`, even when `litellm.max_end_user_budget_id` is configured. So new end users are created with `budget_id = NULL`.

3. **Budget reset job** (`reset_budget_job.py` → `reset_budget_for_litellm_budget_table()`): This job finds budgets past their `reset_at` date, then queries end users with `WHER…