feat(clients): add nim-allographer client with BaraDB driver support

- Pure Nim wire protocol client (async + sync, no C FFI)
- Query Builder: fluent API, SQL generator, execution, transactions
- Schema Builder: create/alter/drop tables, column operations
- Connection pool with aging and timeout handling
- ORM integration via compile-time DB_BARADB switch
- Tests: test_open, test_query
- Documentation: README.md, PLAN_BARADB.md

clients/nim-allographer/example/ddd/repository.nim

@@ -0,0 +1,17 @@
+import json
+import std/asyncdispatch
+import std/options
+import ../../src/allographer/query_builder
+import ../connections
+
+type Repository* = ref object
+  rdb*: SqliteConnections
+
+proc newRepository*(): Repository =
+  Repository(rdb: rdb)
+
+proc getUsers*(this: Repository): seq[JsonNode] =
+  this.rdb.table("users").get().waitFor()
+
+proc getUser*(this: Repository, id: int): Option[JsonNode] =
+  this.rdb.table("users").find(id).waitFor()