feat(core): Engram, Store, Retriever, CLI - Grundsystem Second Brain

- src/engram.py: Gedaechtniseinheit mit Confidence, Correctness, Links
- src/store.py: SQLite FTS5 persistenter Speicher
- src/retriever.py: Hybrid Suche + Reranking
- src/cli.py: Kommandozeilen-Interface

Issue: #1

src/__init__.py

@@ -0,0 +1,8 @@
+"""Second Brain - Gedächtnissystem für OpenClaw."""
+
+from .engram import Engram, Grounding, Correctness, ReviewEntry
+from .store import EngramStore
+from .retriever import Retriever
+
+__version__ = "0.1.0"
+__all__ = ["Engram", "Grounding", "Correctness", "ReviewEntry", "EngramStore", "Retriever"]