feat(raft): transparent leader write/DDL forwarding

- BARADB_RAFT_CLIENT_PEERS maps node id → SQL client host:port
- Followers proxy DML/DDL to the known leader over the wire protocol
  (falls back to "not leader" when the map is missing)
- E2E: follower CREATE/INSERT succeed via forward; docs updated

docs/bg/distributed.md

@@ -16,8 +16,9 @@ Leader election и log репликация през TCP. Включване:
 | `BARADB_RAFT_PORT` | Raft TCP порт |
 | `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) |
+| `BARADB_RAFT_CLIENT_PEERS` | Опционален `id@host:clientPort` map за leader write forwarding |
 
-Когато Raft е активен, SQL DML (`INSERT`/`UPDATE`/`DELETE`/`MERGE` и транзакционен `COMMIT`) и schema DDL (`CREATE`/`DROP`/`ALTER` table, index, view, graph, …) се приемат само от лидера на **`default`** базата. DML отива като put/delete; DDL — като `ddl` запис с оригиналния SQL, преизпълнен на всеки възел при apply. Followers отказват и двете с `not leader; leader is '…'`. Записи към друга database name се отказват. `CREATE`/`DROP DATABASE` не се репликират през raft (multi-DB е извън v1). Приложен DML обновява и secondary B-tree/FTS/HNSW индекси и in-memory графи.
+Когато Raft е активен, SQL DML и schema DDL се приемат само от лидера на **`default`**. DML отива като put/delete; DDL — като `ddl` запис. Followers **препращат** write/DDL към лидера, ако е зададен `BARADB_RAFT_CLIENT_PEERS`; иначе връщат `not leader; leader is '…'`. Записи към друга database name се отказват. `CREATE`/`DROP DATABASE` не се репликират. Приложен DML обновява и secondary индекси/графи.
 
 ```nim
 import barabadb/core/raft

docs/en/distributed.md

@@ -16,8 +16,9 @@ Leader election and log replication over TCP. Enable with:
 | `BARADB_RAFT_PORT` | Raft TCP port |
 | `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) |
+| `BARADB_RAFT_CLIENT_PEERS` | Optional `id@host:clientPort` map for leader write forwarding |
 
-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.
+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 that receive a write/DDL **forward** it to the leader when `BARADB_RAFT_CLIENT_PEERS` maps the leader id to a SQL client address; otherwise they return `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