feat: Remote Nodes Foundation (Strategy B) - Add nodes table with auto-seeded default local node in DatabaseService - Create NodeRegistry service for multi-instance Docker daemon connections - Add 6 Node management API endpoints (CRUD + test connection) - Create NodeManager component with table UI and connection testing - Add NodeContext for frontend-wide active node state management - Add node switcher dropdown to sidebar (visible when >1 node) - Add Nodes tab to Settings Hub

backend/src/services/NodeRegistry.ts

@@ -0,0 +1,150 @@
+import Docker from 'dockerode';
+import { DatabaseService, Node } from './DatabaseService';
+
+/**
+ * NodeRegistry: Manages Docker daemon connections for multiple nodes.
+ * Replaces the old singleton DockerController pattern. Each node
+ * (local or remote) gets its own dedicated Docker client instance.
+ */
+export class NodeRegistry {
+    private static instance: NodeRegistry;
+    private connections: Map<number, Docker> = new Map();
+
+    private constructor() {}
+
+    public static getInstance(): NodeRegistry {
+        if (!NodeRegistry.instance) {
+            NodeRegistry.instance = new NodeRegistry();
+        }
+        return NodeRegistry.instance;
+    }
+
+    /**
+     * Get a Docker client for a specific node.
+     * Creates the connection lazily on first request and caches it.
+     */
+    public getDocker(nodeId: number): Docker {
+        // Return cached connection if available
+        if (this.connections.has(nodeId)) {
+            return this.connections.get(nodeId)!;
+        }
+
+        const db = DatabaseService.getInstance();
+        const node = db.getNode(nodeId);
+
+        if (!node) {
+            throw new Error(`Node with id ${nodeId} not found`);
+        }
+
+        const docker = this.createDockerClient(node);
+        this.connections.set(nodeId, docker);
+        return docker;
+    }
+
+    /**
+     * Get the Docker client for the default node.
+     * This is the backward-compatible path for all existing code.
+     */
+    public getDefaultDocker(): Docker {
+        const db = DatabaseService.getInstance();
+        const defaultNode = db.getDefaultNode();
+
+        if (!defaultNode || !defaultNode.id) {
+            // Absolute fallback: local socket (preserves legacy behavior)
+            return new Docker();
+        }
+
+        return this.getDocker(defaultNode.id);
+    }
+
+    /**
+     * Get the default node ID. Returns the ID of the node marked as default.
+     */
+    public getDefaultNodeId(): number {
+        const db = DatabaseService.getInstance();
+        const defaultNode = db.getDefaultNode();
+        return defaultNode?.id || 1;
+    }
+
+    /**
+     * Create a Docker client based on node configuration.
+     * - Local nodes: use the default socket (Docker autodetects)
+     * - Remote nodes: connect via TCP to host:port
+     */
+    private createDockerClient(node: Node): Docker {
+        if (node.type === 'local') {
+            // Local node: use the default Docker socket
+            return new Docker();
+        }
+
+        // Remote node: connect via Docker TCP API
+        if (!node.host) {
+            throw new Error(`Remote node "${node.name}" is missing a host address`);
+        }
+
+        return new Docker({
+            host: node.host,
+            port: node.port || 2375,
+            // TODO: Phase 55.2 — Add TLS certificate support for secure remote connections
+        });
+    }
+
+    /**
+     * Test connectivity to a specific node.
+     * Returns true if we can ping the Docker daemon.
+     */
+    public async testConnection(nodeId: number): Promise<{ success: boolean; error?: string; info?: any }> {
+        const db = DatabaseService.getInstance();
+        const node = db.getNode(nodeId);
+
+        if (!node) {
+            return { success: false, error: 'Node not found' };
+        }
+
+        try {
+            const docker = this.createDockerClient(node);
+            const info = await docker.info();
+            db.updateNodeStatus(nodeId, 'online');
+            return {
+                success: true,
+                info: {
+                    name: info.Name,
+                    serverVersion: info.ServerVersion,
+                    os: info.OperatingSystem,
+                    architecture: info.Architecture,
+                    containers: info.Containers,
+                    containersRunning: info.ContainersRunning,
+                    images: info.Images,
+                    memTotal: info.MemTotal,
+                    cpus: info.NCPU,
+                }
+            };
+        } catch (error: any) {
+            db.updateNodeStatus(nodeId, 'offline');
+            return { success: false, error: error.message || 'Connection failed' };
+        }
+    }
+
+    /**
+     * Evict a cached connection (e.g., after node config changes).
+     */
+    public evictConnection(nodeId: number): void {
+        this.connections.delete(nodeId);
+    }
+
+    /**
+     * Flush all cached connections.
+     */
+    public flushAll(): void {
+        this.connections.clear();
+    }
+
+    /**
+     * Get the compose directory for a specific node.
+     */
+    public getComposeDir(nodeId: number): string {
+        const db = DatabaseService.getInstance();
+        const node = db.getNode(nodeId);
+        return node?.compose_dir || process.env.COMPOSE_DIR || '/app/compose';
+    }
+}