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

.changeset/add-background-memory-summarization.md

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+---
+"@gsxdsm/fusion": minor
+---
+
+Add background memory summarization and audit processing
+
+This change introduces real-time background processing that automatically extracts and audits project memory insights on a configurable schedule.
+
+**New Features:**
+- Background insight extraction: AI-powered analysis of `.fusion/memory.md` to distill insights into `.fusion/memory-insights.md`
+- Audit reports: Automatic generation of `.fusion/memory-audit.md` after each extraction run
+- Runtime wiring: Both `fn dashboard` and `fn serve` now sync and process insight extraction automation
+
+**Files Generated:**
+- `.fusion/memory-insights.md` — Long-term distilled insights (categories: Patterns, Principles, Conventions, Pitfalls, Context)
+- `.fusion/memory-audit.md` — Human-readable audit report with health checks
+
+**Settings:**
+- `insightExtractionEnabled` — Enable/disable scheduled extraction
+- `insightExtractionSchedule` — Cron expression for extraction timing
+- `insightExtractionMinIntervalMs` — Minimum interval between extractions
+
+**Safety:**
+- Working memory (.fusion/memory.md) is never overwritten
+- Malformed AI output preserves existing insights
+- Post-processing failures are isolated and logged