Fix: Schema version not incremented on followers for CREATE/DROP DATABASE

When CREATE/DROP DATABASE transactions committed on follower nodes, the
DDLSQL field in CommitResult was not set. This caused the replication
handler to skip incrementing the schema version on follower nodes.

Effect: After CREATE DATABASE, subsequent DDL (like CREATE TABLE) would
fail with "schema version mismatch" because followers had version 0 while
coordinator had version 1.

Fix: Return DDLSQL in CommitResult for database operations so followers
increment their schema version correctly.

Verified: WordPress installs and runs correctly on 3-node cluster.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Zohaib Sibte Hassan

db/replication_engine.go

@@ -338,7 +338,15 @@ func (re *ReplicationEngine) Commit(ctx context.Context, req *CommitRequest) *Co
 							Uint64("node_id", re.nodeID).
 							Msg("Database operation committed successfully")
 
-						return &CommitResult{Success: true}
+						// Return DDLSQL so replication handler can increment schema version
+						var ddlSQL string
+						switch dbOp {
+						case DatabaseOpCreate:
+							ddlSQL = fmt.Sprintf("CREATE DATABASE IF NOT EXISTS %s", dbName)
+						case DatabaseOpDrop:
+							ddlSQL = fmt.Sprintf("DROP DATABASE IF EXISTS %s", dbName)
+						}
+						return &CommitResult{Success: true, DDLSQL: ddlSQL}
 					}
 				}
 			}