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/config.py

@@ -55,6 +55,18 @@ class Settings(BaseSettings):
     
     # Generic Redis
     redis_url: str = Field("redis://localhost:6379/0", description="Redis connection URL")
+    redis_sentinel_enabled: bool = Field(False, description="Whether to enable Redis Sentinel")
+    redis_sentinel_nodes: str = Field(
+        "",
+        description="Comma-separated Redis Sentinel nodes, e.g. host1:26379,host2:26379",
+    )
+    redis_sentinel_master_name: str = Field("mymaster", description="Redis Sentinel master name")
+    redis_sentinel_password: str = Field("", description="Password for Redis Sentinel (optional)")
+    redis_sentinel_db: int = Field(0, description="Redis DB index when using Sentinel")
+    redis_sentinel_socket_timeout: float = Field(
+        0.5,
+        description="Socket timeout in seconds for Sentinel clients",
+    )
 
     # Admin console
     enable_admin_console: bool = False
@@ -71,9 +83,43 @@ class Settings(BaseSettings):
             missing.append("SECRET_KEY")
         if not self.database_url:
             missing.append("DATABASE_URL")
+        if self.redis_sentinel_enabled and not self.redis_sentinel_nodes.strip():
+            missing.append("REDIS_SENTINEL_NODES")
         if missing:
             raise ValueError(f"Missing required settings: {', '.join(missing)}")
         return self
 
+    @property
+    def redis_sentinel_hosts(self) -> list[tuple[str, int]]:
+        """Parse Redis Sentinel nodes into (host, port) tuples."""
+        nodes = []
+        raw = self.redis_sentinel_nodes.strip()
+        if not raw:
+            return nodes
+
+        for item in raw.split(","):
+            value = item.strip()
+            if not value:
+                continue
+            if ":" not in value:
+                raise ValueError(f"Invalid sentinel node format: {value}")
+            host, port_text = value.rsplit(":", 1)
+            if not host:
+                raise ValueError(f"Invalid sentinel node host: {value}")
+            try:
+                port = int(port_text)
+            except ValueError as exc:
+                raise ValueError(f"Invalid sentinel node port: {value}") from exc
+            nodes.append((host, port))
+        return nodes
+
+    @property
+    def redis_sentinel_urls(self) -> list[str]:
+        """Build Celery-compatible Sentinel URLs with DB index."""
+        return [
+            f"sentinel://{host}:{port}/{self.redis_sentinel_db}"
+            for host, port in self.redis_sentinel_hosts
+        ]
+
 
 settings = Settings()