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/src/allographer/utils.nim

@@ -0,0 +1,13 @@
+import strutils
+
+func getOsName*():string =
+  when defined(linux) or defined(bsd):
+    const f = staticRead("/etc/os-release")
+    for row in f.split("\n"):
+      let kv = row.split("=")
+      if kv[0] == "ID":
+        return kv[1]
+  elif defined(windows):
+    return "windows"
+  else:
+    return ""