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/sqlite/test_pool_wait.nim

@@ -0,0 +1,25 @@
+discard """
+  cmd: "nim c -d:reset -d:ssl -r $file"
+"""
+
+import std/[asyncdispatch, os, strutils, unittest]
+import ../../src/allographer/connection
+import ../../src/allographer/query_builder
+
+
+suite "SQLite pool waiter (notify)":
+  test "pool size 1: two concurrent raw gets both complete":
+    let sqliteHost = getEnv("SQLITE_HOST")
+    let timeout = getEnv("DB_TIMEOUT").parseInt
+    let rdb = dbOpen(SQLite3, sqliteHost, maxConnections = 1, timeout)
+    proc sel(): Future[void] {.async.} =
+      discard await rdb.raw("SELECT 1").get()
+    let a = sel()
+    let b = sel()
+    waitFor all(a, b)
+
+  test "pool size 0: raw get raises DbError":
+    let sqliteHost = getEnv("SQLITE_HOST")
+    let rdb = dbOpen(SQLite3, sqliteHost, maxConnections = 0, timeout = 0)
+    expect(DbError):
+      discard waitFor rdb.raw("SELECT 1").get()