Replace local TOML loading with mcdsl/config.Load[Config] which adds
METACRYPT_ environment variable overrides. ServerConfig and MCIASConfig
now embed their mcdsl counterparts, extending with ExternalURL and
ServiceToken respectively. DatabaseConfig and LogConfig replaced with
mcdsl types directly.
TOML structure is preserved — no config file changes needed.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>