Features:
- FFF (fff-node) integrated as optional dependency for SIMD-accelerated search
- find/grep: FFF-first with SDK fallback
- multi_grep: Aho-Corasick OR search (FFF-only)
- /fff-health and /fff-rescan commands
- Session lifecycle hooks (session_start/session_shutdown)

Architecture:
- Optional dependency — graceful fallback if FFF unavailable
- FFF output → ripgrep format conversion (zero changes to pretty rendering)
- Verified: @ff-labs/fff-node binary SHA256 matches GitHub release