feat: add HA infrastructure, CI/CD pipeline, and Redis/Celery hardening

- Add docker-compose.ha.yml for PostgreSQL/Redis HA setup with Patroni and Sentinel
- Add docker-compose.prod.yml for production deployment
- Add GitHub Actions CI/CD workflow (build.yml)
- Add install.cmd for Windows one-click setup
- Harden Redis connection with retry logic and health checks
- Add Celery HA config with Redis Sentinel support
- Add HA operations runbook
- Update README with deployment and architecture docs
- Move landing page spec to .claude/specs/design/
- Update memory intelligence PRD

backend/app/core/redis.py

@@ -1,25 +1,46 @@
 """Redis client module."""
 
-from typing import AsyncGenerator
-
 from redis.asyncio import Redis, from_url
+from redis.asyncio.sentinel import Sentinel
 
 from app.core.config import settings
+from app.core.logging import get_logger
 
 _redis_pool: Redis | None = None
+_sentinel_pool: Sentinel | None = None
+logger = get_logger(__name__)
 
 
 async def get_redis() -> Redis:
     """Get global Redis client instance."""
-    global _redis_pool
+    global _redis_pool, _sentinel_pool
     if _redis_pool is None:
-        _redis_pool = from_url(settings.redis_url, encoding="utf-8", decode_responses=True)
+        if settings.redis_sentinel_enabled:
+            _sentinel_pool = Sentinel(
+                settings.redis_sentinel_hosts,
+                socket_timeout=settings.redis_sentinel_socket_timeout,
+                password=settings.redis_sentinel_password or None,
+                decode_responses=True,
+            )
+            _redis_pool = _sentinel_pool.master_for(
+                settings.redis_sentinel_master_name,
+                db=settings.redis_sentinel_db,
+                decode_responses=True,
+            )
+            logger.info(
+                "redis_connected_via_sentinel",
+                master_name=settings.redis_sentinel_master_name,
+                sentinel_nodes=settings.redis_sentinel_nodes,
+            )
+        else:
+            _redis_pool = from_url(settings.redis_url, encoding="utf-8", decode_responses=True)
     return _redis_pool
 
 
 async def close_redis():
     """Close Redis connection."""
-    global _redis_pool
+    global _redis_pool, _sentinel_pool
     if _redis_pool:
         await _redis_pool.close()
         _redis_pool = None
+    _sentinel_pool = None