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/migrations/init_databaase.nim

@@ -0,0 +1,23 @@
+import ../../../src/allographer/schema_builder
+import ../connection
+
+proc initDatabaase*() =
+  ## 0001
+  rdb.create([
+    table("user", [
+      Column.uuid("id").index().comment("User ID"),
+      Column.string("name").comment("User name"),
+      Column.string("email").comment("User email address"),
+      Column.string("password").comment("User password"),
+      Column.integer("created_at").index().comment("Created at"),
+      Column.integer("updated_at").index().comment("Updated at"),
+    ], "User table"),
+    table("post", [
+      Column.uuid("id").index().comment("Post ID"),
+      Column.string("title").comment("Post title"),
+      Column.string("content").comment("Post content"),
+      Column.strForeign("user_id").reference("id").onTable("user").comment("User ID"),
+      Column.integer("created_at").index().comment("Created at"),
+      Column.integer("updated_at").index().comment("Updated at"),
+    ], "Post table"),
+  ])