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/database/connection.nim

@@ -0,0 +1,17 @@
+import std/asyncdispatch
+import std/os
+import std/strutils
+import ../../src/allographer/connection
+
+let
+  pgUrl = getEnv("PG_URL")
+  mariaUrl = getEnv("MARIA_URL")
+  mysqlUrl = getEnv("MYSQL_URL")
+  maxConnections = getEnv("DB_MAX_CONNECTION").parseInt
+  timeout = getEnv("DB_TIMEOUT").parseInt
+
+# let rdb* = dbOpen(SQLite3, "./db.sqlite3", shouldDisplayLog=true)
+let rdb* = dbOpen(PostgreSQL, pgUrl, maxConnections, timeout, shouldDisplayLog=true)
+# let rdb* = dbOpen(Mariadb, mariaUrl, maxConnections, timeout, shouldDisplayLog=true)
+# let rdb* = dbOpen(MySQL, mysqlUrl, maxConnections, timeout, shouldDisplayLog=true)
+# let rdb* = dbOpen(SurrealDB, "test", "test", "user", "pass", "http://surreal", 8000, 5, 30, shouldDisplayLog=true).waitFor()