fix: comprehensive audit fixes for dashboard and backend

Backend:
- Emit WebSocket events from REST delete/promote/demote handlers
- Emit DreamStarted/ConsolidationStarted from MCP tool dispatch
- Add path validation in backup_to() for defense-in-depth

Dashboard:
- Fix ConnectionDiscovered field names (source_id/target_id)
- Fix $effect → onMount in settings (prevents infinite loop)
- Fix $derived → $derived.by in RetentionCurve
- Fix field name mismatches in settings (nodesProcessed, etc.)
- Fix nested <button> → <span role="button"> in memories
- Fix unhandled Promise rejection in stats consolidation
- Add missing EVENT_TYPE_COLORS entries
- Add Three.js resource disposal and event listener cleanup
- Eliminate duplicate root page, redirect to /graph
- Update nav links and keyboard shortcuts to /graph

All 734+ tests passing, 22MB binary, zero build warnings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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