Unify NostrUser and Author nodes; add migrations support

Merged 'Author' nodes into 'NostrUser' for unified identity tracking and social graph representation. Introduced migrations framework to handle schema changes, including retroactive updates for existing relationships and constraints. Updated tests, schema definitions, and documentation to reflect these changes.

pkg/neo4j/fetch-event_test.go

@@ -331,7 +331,7 @@ func TestGetSerialsByIds(t *testing.T) {
 	}
 
 	// Create and save multiple events
-	ids := tag.NewS()
+	ids := tag.New()
 	for i := 0; i < 3; i++ {
 		ev := event.New()
 		ev.Pubkey = signer.Pub()
@@ -347,7 +347,8 @@ func TestGetSerialsByIds(t *testing.T) {
 			t.Fatalf("Failed to save event: %v", err)
 		}
 
-		ids.Append(tag.NewFromAny("", hex.Enc(ev.ID[:])))
+		// Append ID to the tag's T slice
+		ids.T = append(ids.T, []byte(hex.Enc(ev.ID[:])))
 	}
 
 	// Get serials by IDs