fix(raft): graph apply + reject non-default DB writes

- applyReplicatedPut/Delete keep in-memory graphs in sync with node/edge
  table rows (idempotent edges via addEdgeWithIdIfAbsent).
- When Raft is enabled, DML is refused on any database other than
  'default' (the only DB the state machine is wired to).
- Docs updated (en/bg); unit test for graph apply.

docs/bg/distributed.md

@@ -17,7 +17,7 @@ Leader election и log репликация през TCP. Включване:
 | `BARADB_RAFT_PEERS` | Списък `id@host:port` (вкл. себе си) |
 | `BARADB_RAFT_WRITE_TIMEOUT_MS` | Макс. изчакване за majority commit при SQL записи (по подразбиране 5000) |
 
-Когато Raft е активен, SQL DML (`INSERT`/`UPDATE`/`DELETE`/`MERGE` и транзакционен `COMMIT`) се приема само от лидера: KV двойките се добавят в Raft лога и клиентът чака majority commit. Followers отказват записи с `not leader; leader is '…'`. Приложените записи отиват в **default** базата. DDL (напр. `CREATE TABLE`) още не се репликира — схемата трябва да се създаде на всеки възел.
+Когато Raft е активен, SQL DML (`INSERT`/`UPDATE`/`DELETE`/`MERGE` и транзакционен `COMMIT`) се приема само от лидера на **`default`** базата: KV двойките се добавят в Raft лога и клиентът чака majority commit. Followers отказват записи с `not leader; leader is '…'`. Записи към друга database name се отказват (`raft writes only supported on the 'default' database`). Приложените записи обновяват LSM + secondary B-tree/FTS/HNSW индекси и in-memory графи на всеки възел. DDL (напр. `CREATE TABLE`) още не се репликира — схемата трябва да се създаде на всеки възел.
 
 ```nim
 import barabadb/core/raft

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: 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 '…'`. Followers apply committed entries via `applyCommand` into the **default** database. 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`) 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.
 
 ```nim
 import barabadb/core/raft