feat(display): document and test memory_notifications setting

Follow-up to salvaged PR #4684:
- Add display.memory_notifications to DEFAULT_CONFIG (off|on|verbose, default on)
- Document the setting in docs/user-guide/features/memory.md
- Add resolver tests for off/on/verbose memory + skill paths

hermes_cli/config.py

@@ -1428,6 +1428,12 @@ DEFAULT_CONFIG = {
         "tui_agents_nudge": True,
         "bell_on_complete": False,
         "show_reasoning": False,
+        # Background self-improvement review notifications surfaced in chat.
+        #   "off"     — no chat notification (the review still runs and writes)
+        #   "on"      — generic "💾 Memory updated" line (default)
+        #   "verbose" — include a compact content preview of what changed
+        # Per-platform overrides via display.platforms.<platform>.memory_notifications.
+        "memory_notifications": "on",
         "streaming": False,
         "timestamps": False,      # Show [HH:MM] on user and assistant labels
         "final_response_markdown": "strip",  # render | strip | raw