Add web dashboard (axum) on port 3927 with memory browser, search, and
system stats. New MCP tools: memory_timeline, memory_changelog,
health_check, consolidate, stats, backup, export, gc. Search now supports
detail_level (brief/summary/full) to control token usage. Add backup_to()
and get_recent_state_transitions() to storage layer. Bump to v1.2.0.
