refactor: remove redis sentinel support and simplify redis connection handling

[l50]

Key Changes:

• Removed all Redis Sentinel-specific logic and configuration from codebase
• Refactored Redis client helpers to support only direct Redis connections
• Updated connection/reconnection logic to eliminate Sentinel DNS/IP refresh
• Simplified tests and documentation to reflect direct Redis usage only

Added:

• Manual test guide for multi-forest end-to-end operations (unrelated to
  Sentinel removal, but included in this change for completeness) -
  docs/testing/MANUAL-ESSOS.md documents manual steps for multi-domain attack
  chains

• New manual test guide for multi-forest/Essos compromise workflow, including
  all operational steps, troubleshooting, and known issues

Changed:

• Redis client creation helpers (create_redis_client, create_verified_redis_client)
  now use only direct Redis URL connections with optional single-connection mode

• All references to "Sentinel" failover, stale connections, or master discovery
  replaced with generic Redis connection handling and pod restart recovery

• Logging, comments, and error messages updated to no longer mention Sentinel

• Task queue, orchestrator, and dispatcher logic refactored to remove
  Sentinel-specific reconnection and state reset paths

• Documentation (codemap.md, inline code docs) updated to reflect removal
  of Sentinel features and clarify direct Redis usage

• All Redis-related health check, retry, and reconnection logic now targets
  direct connections, not Sentinel pools or master/replica roles

• Tests updated to remove patching and assertions related to
  invalidate_sentinel_client and Sentinel failover scenarios

• Env var documentation and code references updated to reflect direct Redis use

Removed:

• All Redis Sentinel support, including:
  • Sentinel connection pooling, master/replica discovery, and DNS resolution
  • invalidate_sentinel_client function and calls throughout codebase
  • Sentinel-related configuration and environment variable handling
  • Replica client and master role verification logic
  • Documentation and comments referencing Sentinel failover or pod restarts
• Sentinel-specific error handling and reconnection logic in orchestration,
  task queues, dispatcher monitoring, and recovery modules
• Sentinel handling and patching from all tests and test fixtures
• Redis Sentinel configuration, DNS resolution, and all related branching logic
• All code and tests for verifying master/replica roles and Sentinel failover
• Sentinel-specific error keywords and handling logic across modules and tests