[feat] setup master from fork with fastapi + otel

docs/002-config-yaml-plus-env.md

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+# 002 Config From YAML and Env
+
+Context
+- The service needs readable project configuration and safe handling of sensitive values.
+- The final configuration object should be easy to inject and test.
+
+Decision
+- Keep non-sensitive defaults in YAML files under `config/`.
+- Read sensitive values only from environment variables.
+- Merge YAML and env sources into one `AppConfig` dataclass tree in `adapter/config/`.
+- Keep configuration parsing and validation outside `domain/` and `usecase/`.
+
+Consequences
+- Local configuration remains simple to inspect and version.
+- Secrets stay out of committed files.
+- Inner layers depend on typed config data, not on env or YAML readers.