feat(FN-1399): add background memory summarization after task completion

- Add MemoryInsights class in @fusion/core for AI-powered memory audit generation
- Add post-run hook to CronRunner for triggering memory summarization after scheduled tasks
- Wire memory background processing in both dashboard and serve commands
- Add memoryAuditEnabled and memoryAuditSchedule settings for configurable automation
- Fix startup ordering: sync automation before cronRunner.start() to prevent race conditions
- Add comprehensive tests for memory-insights and dashboard/serve integration
- Update contributing.md and settings-reference.md with documentation

docs/contributing.md

@@ -97,6 +97,15 @@ When enabled, agents can read/write durable project memory:
 
 Use it for reusable patterns, constraints, and pitfalls that should persist across tasks.
 
+### Background Memory Summarization
+
+Fusion can automatically extract insights from working memory and distill them into long-term memory. Enable via `insightExtractionEnabled` setting:
+
+- `.fusion/memory-insights.md` — Long-term distilled insights
+- `.fusion/memory-audit.md` — Audit report after each extraction run
+
+See [Settings Reference](./settings-reference.md#background-memory-summarization--audit) for configuration details.
+
 ## SQLite Test Runner Pitfall
 
 When running engine tests with Vitest and `node:sqlite`, ensure the engine Vitest config uses thread pool mode: