init: Engram v0.1 — native memory substrate for accumulating intelligence

Memory is not stored and retrieved — it is activated and propagated.
Implements the spreading activation model with salience decay, typed edges,
four memory tiers, and flat cosine vector search over a sled embedded store.

.gitignore

@@ -0,0 +1,3 @@
+target/
+*.db
+.DS_Store