BasePostgresConfig defaults use_orjson_serialization=True, so the [settings] install from the quick start fails with ImportError #59

Versions: sqlalchemy-foundation-kit 0.4.0 (same code on master, adcd645), SQLAlchemy 2.0.54, asyncpg 0.31.0, pydantic 2.13.5, pydantic-settings 2.15.0, Python 3.13.12; orjson not installed

BasePostgresConfig.use_orjson_serialization defaults to True (contrib/settings/postgres.py:135-138), but orjson ships only with the orjson and all extras (pyproject.toml:52-54). The quick start installs sqlalchemy-foundation-kit[settings] ("recommended", docs/guide/quickstart.md:13-14) or [settings,metrics], then builds a config with defaults and calls create_async_session_manager. That fails with ImportError before anything connects. The dishka and dependency-injector integrations call create_async_session_manager(postgres_config, ...) too (contrib/di/database.py:88, contrib/dependency_injector/database.py:40, 161), so they hit the same error. Every other entry point defaults the other way: AsyncSessionManager(use_orjson=False) (session/manager.py:235) and the builder (session/builder.py:76). Only the settings path assumes an optional dependency.

Reproduction

With pip install "sqlalchemy-foundation-kit[settings]":

from pydantic import SecretStr
from sqlalchemy_foundation_kit import create_async_session_manager
from sqlalchemy_foundation_kit.contrib.settings import BasePostgresConfig, ConnectionSettings

# pip install "sqlalchemy-foundation-kit[settings]"  -- the install the quick start recommends
config = BasePostgresConfig(
    connection=ConnectionSettings(password=SecretStr("secret"), database="app"),
    application_name="my-service",
)
print("use_orjson_serialization =", config.use_orjson_serialization)
create_async_session_manager(config)  # builds the engine, does not connect
print("manager created")

Actual

use_orjson_serialization = True
Traceback (most recent call last):
  ...
  File ".../sqlalchemy_foundation_kit/session/factories.py", line 101, in create_async_session_manager
  File ".../sqlalchemy_foundation_kit/session/manager.py", line 278, in __init__
  File ".../sqlalchemy_foundation_kit/base/engine.py", line 203, in build_engine_kwargs
  File ".../sqlalchemy_foundation_kit/base/serialization.py", line 85, in configure_orjson_serialization
  File ".../sqlalchemy_foundation_kit/base/_optional.py", line 31, in require_optional
ImportError: orjson is required for this functionality. Install it with: pip install 'sqlalchemy-foundation-kit[orjson]'

The message is clear, but anyone following the quick start hits it first, and it is about a feature that matters only to services with JSON/JSONB columns.

Why

create_async_session_manager passes use_orjson=postgres_config.use_orjson_serialization (session/factories.py:108). build_engine_kwargs then imports orjson unconditionally when the flag is set (base/engine.py:200-203).

Proposal

Default use_orjson_serialization to False, matching AsyncSessionManager and the builder. The serializer is opt-in everywhere else, and turning it on changes how JSON columns serialize (orjson's handling of datetime, non-str keys and Decimal via the kit's default encoder differs from json.dumps), so it is better as an explicit choice than as something that happens because orjson is installed. Update the defaults table (docs/guide/configuration.md:288), the docs/agents.md:311 row and the README's protocol example (README.md:149). Adding orjson to the settings extra would also fix the error, but it would tie a serialization choice to the configuration extra.