feat(#71): implement graph data API

Implemented three new API endpoints for knowledge graph visualization:

1. GET /api/knowledge/graph - Full knowledge graph
   - Returns all entries and links with optional filtering
   - Supports filtering by tags, status, and node count limit
   - Includes orphan detection (entries with no links)

2. GET /api/knowledge/graph/stats - Graph statistics
   - Total entries and links counts
   - Orphan entries detection
   - Average links per entry
   - Top 10 most connected entries
   - Tag distribution across entries

3. GET /api/knowledge/graph/:slug - Entry-centered subgraph
   - Returns graph centered on specific entry
   - Supports depth parameter (1-5) for traversal distance
   - Includes all connected nodes up to specified depth

New Files:
- apps/api/src/knowledge/graph.controller.ts
- apps/api/src/knowledge/graph.controller.spec.ts

Modified Files:
- apps/api/src/knowledge/dto/graph-query.dto.ts (added GraphFilterDto)
- apps/api/src/knowledge/entities/graph.entity.ts (extended with new types)
- apps/api/src/knowledge/services/graph.service.ts (added new methods)
- apps/api/src/knowledge/services/graph.service.spec.ts (added tests)
- apps/api/src/knowledge/knowledge.module.ts (registered controller)
- apps/api/src/knowledge/dto/index.ts (exported new DTOs)
- docs/scratchpads/71-graph-data-api.md (implementation notes)

Test Coverage: 21 tests (all passing)
- 14 service tests including orphan detection, filtering, statistics
- 7 controller tests for all three endpoints

Follows TDD principles with tests written before implementation.
All code quality gates passed (lint, typecheck, tests).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/orchestrator/src/valkey/valkey.service.ts

@@ -0,0 +1,132 @@
+import { Injectable, OnModuleDestroy } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { ValkeyClient, ValkeyClientConfig } from './valkey.client';
+import type {
+  TaskState,
+  AgentState,
+  TaskStatus,
+  AgentStatus,
+  OrchestratorEvent,
+  EventHandler,
+  TaskContext,
+} from './types';
+
+/**
+ * NestJS service for Valkey state management and pub/sub
+ */
+@Injectable()
+export class ValkeyService implements OnModuleDestroy {
+  private readonly client: ValkeyClient;
+
+  constructor(private readonly configService: ConfigService) {
+    const config: ValkeyClientConfig = {
+      host: this.configService.get<string>('orchestrator.valkey.host', 'localhost'),
+      port: this.configService.get<number>('orchestrator.valkey.port', 6379),
+    };
+
+    const password = this.configService.get<string>('orchestrator.valkey.password');
+    if (password) {
+      config.password = password;
+    }
+
+    this.client = new ValkeyClient(config);
+  }
+
+  async onModuleDestroy(): Promise<void> {
+    await this.client.disconnect();
+  }
+
+  /**
+   * Task State Management
+   */
+
+  async getTaskState(taskId: string): Promise<TaskState | null> {
+    return this.client.getTaskState(taskId);
+  }
+
+  async setTaskState(state: TaskState): Promise<void> {
+    return this.client.setTaskState(state);
+  }
+
+  async deleteTaskState(taskId: string): Promise<void> {
+    return this.client.deleteTaskState(taskId);
+  }
+
+  async updateTaskStatus(
+    taskId: string,
+    status: TaskStatus,
+    agentId?: string,
+    error?: string
+  ): Promise<TaskState> {
+    return this.client.updateTaskStatus(taskId, status, agentId, error);
+  }
+
+  async listTasks(): Promise<TaskState[]> {
+    return this.client.listTasks();
+  }
+
+  /**
+   * Agent State Management
+   */
+
+  async getAgentState(agentId: string): Promise<AgentState | null> {
+    return this.client.getAgentState(agentId);
+  }
+
+  async setAgentState(state: AgentState): Promise<void> {
+    return this.client.setAgentState(state);
+  }
+
+  async deleteAgentState(agentId: string): Promise<void> {
+    return this.client.deleteAgentState(agentId);
+  }
+
+  async updateAgentStatus(
+    agentId: string,
+    status: AgentStatus,
+    error?: string
+  ): Promise<AgentState> {
+    return this.client.updateAgentStatus(agentId, status, error);
+  }
+
+  async listAgents(): Promise<AgentState[]> {
+    return this.client.listAgents();
+  }
+
+  /**
+   * Event Pub/Sub
+   */
+
+  async publishEvent(event: OrchestratorEvent): Promise<void> {
+    return this.client.publishEvent(event);
+  }
+
+  async subscribeToEvents(handler: EventHandler): Promise<void> {
+    return this.client.subscribeToEvents(handler);
+  }
+
+  /**
+   * Convenience methods
+   */
+
+  async createTask(taskId: string, context: TaskContext): Promise<void> {
+    const now = new Date().toISOString();
+    const state: TaskState = {
+      taskId,
+      status: 'pending',
+      context,
+      createdAt: now,
+      updatedAt: now,
+    };
+    await this.setTaskState(state);
+  }
+
+  async createAgent(agentId: string, taskId: string): Promise<void> {
+    const state: AgentState = {
+      agentId,
+      status: 'spawning',
+      taskId,
+    };
+    await this.setAgentState(state);
+  }
+}