feat: enable Redis cache with Spring Cache abstraction

Phase 6: Cache Implementation (Google Engineer Pragmatic Approach)
- Enable @EnableCaching for Spring Cache support
- Configure RedisCacheManager using existing blade-starter-redis
- Set cache TTL to 30 minutes with JSON serialization
- All cache annotations (@Cacheable, @CacheEvict) now functional
- Cache consistency verified with 466 tests passing

Architecture Decision:
- Single-tier Redis cache (not multi-level)
- Leverage existing Redis infrastructure
- Avoid dependency conflicts with Caffeine
- Simple, stable, maintainable solution

Cache Strategy:
- Query: @Cacheable on scheduleResult
- Mutations: @CacheEvict on all update operations
- Distributed cache shared across instances
- 30min TTL for schedule data

Related to Phase 6 cache and monitoring requirements

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