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

docs/en/distributed.md

@@ -17,7 +17,7 @@ Leader election and log replication over TCP. Enable with:
 | `BARADB_RAFT_PEERS` | Comma-separated `id@host:port` (include self) |
 | `BARADB_RAFT_WRITE_TIMEOUT_MS` | Max wait for majority commit on SQL writes (default 5000) |
 
-When Raft is enabled, SQL DML (`INSERT`/`UPDATE`/`DELETE`/`MERGE` and transactional `COMMIT`) is accepted only on the leader of the **`default`** database: each write's KV pairs are appended to the Raft log and the client waits until the entry is majority-committed. Followers reject writes with `not leader; leader is '…'`. Writes against any other database name are rejected (`raft writes only supported on the 'default' database`). Committed entries update LSM plus secondary B-tree/FTS/HNSW indexes and in-memory graphs on every node. DDL (e.g. `CREATE TABLE`) is not replicated yet — apply schema on every node.
+When Raft is enabled, SQL DML (`INSERT`/`UPDATE`/`DELETE`/`MERGE` and transactional `COMMIT`) and schema DDL (`CREATE`/`DROP`/`ALTER` table, index, view, graph, …) are accepted only on the leader of the **`default`** database. DML ships as put/delete log entries; DDL ships as a `ddl` entry with the original SQL and is re-executed on every node at apply. Followers reject both with `not leader; leader is '…'`. Writes against any other database name are rejected (`raft writes only supported on the 'default' database`). `CREATE`/`DROP DATABASE` are not raft-replicated (multi-DB is out of scope for v1). Committed DML also updates secondary B-tree/FTS/HNSW indexes and in-memory graphs.
 
 ```nim
 import barabadb/core/raft