feat: Add Prolog-based memory system for agents

- Add prolog_memory.py with Prolog rules for memory classification
- Agent functions: query_memory, classify_memory, preserve_memory
- Full memory ontology with importance scores 1-5
- Relationship tracking and dependency rules
- SimpleClassifier fallback when Prolog not available
- pip install memtext[prolog] enables Prolog engine

Author: Memtext User