Migrate RedisLock implementation to valkey-glide

## Objective

Migrate the distributed locking implementation from redis-py's AsyncRedisLock to valkey-glide.

## Files to modify

- `src/ai/backend/common/lock.py` (lines 205-272)
- `RedisLock` class implementation

## Tasks

- [ ] Research valkey-glide's distributed locking capabilities
- [ ] Implement distributed lock using valkey-glide client
- [ ] Replace redis-py imports with valkey-glide equivalents
- [ ] Ensure lock semantics remain compatible (acquire, release, timeout)
- [ ] Update type annotations

## Dependencies

This is the core migration task that other tasks depend on.

## Related

Part of BA-2585 - Retire redis-py entirely

JIRA Issue: BA-3266