[loop-cycle-151] refactor: extract embedding functions to memory/embeddings.py (#344) (#355)

src/timmy/memory/__init__.py

@@ -1 +1,7 @@
-"""Memory — Persistent conversation and knowledge memory."""
+"""Memory — Persistent conversation and knowledge memory.
+
+Sub-modules:
+    embeddings  — text-to-vector embedding + similarity functions
+    unified     — unified memory schema and connection management
+    vector_store — backward compatibility re-exports from memory_system
+"""