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/migrate.nim

@@ -0,0 +1,41 @@
+import json
+import ../src/allographer/schema_builder
+import connections
+
+
+# migration
+rdb.create([
+  table("Auth",[
+    Column.increments("id"),
+    Column.string("auth")
+  ]),
+  table("Users",[
+    Column.increments("id"),
+    Column.uuid("uuid"),
+    Column.string("oid").index().nullable(),
+    Column.string("oid2").index().nullable(),
+    Column.string("Name").nullable(),
+    Column.date("birth_date").nullable(),
+    Column.foreign("auth_id").reference("id").onTable("Auth").onDelete(SET_NULL).default(1)
+  ]),
+])
+
+rdb.alter([
+  table("Users", [
+    # add column
+    Column.string("aaa").default("").add(),
+    Column.foreign("bbb").reference("id").onTable("Auth").onDelete(SET_NULL).add(),
+    # change column definition
+    Column.string("aaa").nullable().change(),
+    # change column name
+    Column.renameColumn("aaa", "ccc"),
+    # delete column
+    Column.dropColumn("ccc"),
+    Column.dropColumn("bbb"),
+  ]),
+  # change table name
+  table("Users").renameTo("members"),
+])
+
+# drop table
+rdb.drop(table("members"))