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/config/orchestrator.config.ts

@@ -5,6 +5,7 @@ export const orchestratorConfig = registerAs("orchestrator", () => ({
   valkey: {
     host: process.env.VALKEY_HOST ?? "localhost",
     port: parseInt(process.env.VALKEY_PORT ?? "6379", 10),
+    password: process.env.VALKEY_PASSWORD,
     url: process.env.VALKEY_URL ?? "redis://localhost:6379",
   },
   claude: {
@@ -22,5 +23,9 @@ export const orchestratorConfig = registerAs("orchestrator", () => ({
   },
   sandbox: {
     enabled: process.env.SANDBOX_ENABLED === "true",
+    defaultImage: process.env.SANDBOX_DEFAULT_IMAGE ?? "node:20-alpine",
+    defaultMemoryMB: parseInt(process.env.SANDBOX_DEFAULT_MEMORY_MB ?? "512", 10),
+    defaultCpuLimit: parseFloat(process.env.SANDBOX_DEFAULT_CPU_LIMIT ?? "1.0"),
+    networkMode: process.env.SANDBOX_NETWORK_MODE ?? "bridge",
   },
 }));