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/tests/baradb/test_open.nim

@@ -0,0 +1,13 @@
+discard """
+  cmd: "nim c $file"
+"""
+
+import std/unittest
+import ../../src/allographer/connection
+import ../../src/allographer/query_builder
+
+
+suite("Baradb connection"):
+  test("connection"):
+    let rdb = dbOpen(Baradb, "default", "admin", "", "127.0.0.1", 9472)
+    check(rdb.isConnected())