feat(raft): replicate schema DDL through the raft log

- isRaftDdl + leader-only gate for CREATE/DROP/ALTER (not DATABASE)
- appendDdlToRaft ships original SQL; applyCommand re-executes via
  applyReplicatedDdl (idempotent on leader double-apply)
- Mixed DDL+DML batches use the DDL path so order is preserved
- Fix secondary-index point lookup to use entry.lsmKey (not filter col)
- E2E: CREATE only on leader, schema + index SELECT on follower

src/barabadb/query/exec/dml.nim

@@ -488,3 +488,11 @@ proc applyReplicatedDelete*(ctx: ExecutionContext, fullKey: string) =
   if found and table.len > 0:
     removeIndexesForRow(ctx, table, fullKey, cast[string](existing))
   ctx.db.delete(fullKey)
+
+proc isBenignRaftReplayError*(msg: string): bool =
+  ## Leader re-applies committed DDL/DML after local execution; followers may
+  ## also see IF EXISTS / race re-applies. Treat common idempotent failures as OK.
+  let m = msg.toLower()
+  "already exists" in m or "does not exist" in m or
+    "duplicate" in m or "unique" in m or
+    "unknown table" in m or "no such table" in m

src/barabadb/query/exec/params.nim

@@ -179,6 +179,17 @@ proc isDDL*(stmt: Node): bool =
   else:
     result = false
 
+proc isRaftDdl*(stmt: Node): bool =
+  ## Schema changes that go through the Raft log when clustering is on.
+  ## CREATE/DROP DATABASE are excluded — multi-DB is out of scope for v1 raft
+  ## (state machine is wired only to the default database).
+  if not isDDL(stmt): return false
+  case stmt.kind
+  of nkCreateDatabase, nkDropDatabase:
+    result = false
+  else:
+    result = true
+
 proc isWrite*(stmt: Node): bool =
   ## True for statements that mutate stored data. `nkCommitTxn` is included
   ## because COMMIT emits the transaction's buffered kvPairs.