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/utils/test_database_url.nim

@@ -0,0 +1,42 @@
+discard """
+  cmd: "nim c -d:reset $file"
+"""
+
+import std/unittest
+import ../../src/allographer/query_builder/libs/database_url
+
+
+suite("database url"):
+  test("parse query and credentials"):
+    let url = parseDatabaseUrl(
+      "postgresql://user%40mail:pa%3Ass@host:5432/db%2Fname?sslmode=require&application_name=allographer"
+    )
+
+    check url.scheme == "postgresql"
+    check url.username == "user@mail"
+    check url.password == "pa:ss"
+    check url.hostname == "host"
+    check url.hasPort
+    check url.port == 5432
+    check url.databaseName == "db/name"
+    check url.query == @[
+      (key: "sslmode", value: "require"),
+      (key: "application_name", value: "allographer"),
+    ]
+
+
+  test("postgres alias stays valid"):
+    let url = parseDatabaseUrl("postgres://user:pass@host:5432/database")
+    check url.scheme == "postgres"
+
+
+  test("port defaults are explicit"):
+    let url = parseDatabaseUrl("mysql://user:pass@host/database")
+    check not url.hasPort
+    check portOrDefault(url, 3306) == 3306
+
+
+  test("sqlite path from url"):
+    let url = parseDatabaseUrl("sqlite://./relative/path.db")
+    check sqliteDatabasePath(url) == "./relative/path.db"
+    check sqliteDatabasePath(parseDatabaseUrl("sqlite://relative/path.db")) == "relative/path.db"