Distinguish optional service error state

[codeforester]

Summary

• Add an error state for optional services that have start evidence but fail health checks.
• Preserve stopped for optional services with no process state file or compose state.
• Report optional service errors from services check with a non-zero exit.
• Add BATS coverage for process state, compose state, and deterministic no-state checks.

Validation

• ./tests/validate.sh
• bats tests/services_test.bats
• bats tests/infra_test.bats
• bats tests/native_services_test.bats
• BASE_DEMO_SERVICES_STATE_DIR=$(mktemp -d "${TMPDIR:-/tmp}/base-demo-status.XXXXXX") BASE_DEMO_SERVICES_DRY_RUN=1 ./bin/base-demo-services status
• env GRADLE_USER_HOME=/private/tmp/base-demo-gradle-89 bats tests/demo_test.bats tests/services_test.bats tests/environments_test.bats tests/infra_test.bats tests/go_api_test.bats tests/python_api_test.bats tests/java_services_test.bats tests/native_services_test.bats tests/demo_console_test.bats
• git diff --check

Note: the full BATS run used a fresh Gradle user home with escalated local execution because sandboxed Gradle initialization hit a local socket restriction.

Fixes #89