Migrate redis_helper.py connection management to valkey-glide

## Objective

Migrate central Redis connection management and command execution wrapper from redis-py to valkey-glide.

## Files to modify

- `src/ai/backend/common/redis_helper.py`
- Lines 21-35: Import statements
- Lines 84-190: `execute()` function - command execution with retry logic
- Lines 213-304: `get_redis_object()` function - connection factory

## Tasks

- [ ] Replace redis-py client types with valkey-glide equivalents
- [ ] Migrate `execute()` function retry and error handling logic
- [ ] Update `get_redis_object()` to create valkey-glide clients
- [ ] Handle Redis Sentinel configuration if applicable
- [ ] Update exception handling for valkey-glide

## Related

Part of BA-2585 - Retire redis-py entirely

JIRA Issue: BA-3267