fix: make external node compose portable

[ayaanoncrypto]

Addresses issue #6.

Make the external-node Compose file portable across current Compose implementations. Remove the legacy-incompatible top-level name field and quote the boolean pruning environment value so interpolation preserves a string-compatible value.

Validation:

• YAML parsing passed.
• • Compose structure check passed: five services, no top-level name, and string-compatible pruning value.
• • git diff --check passed.

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PR-Codex overview

This PR focuses on updating the EN_PRUNING_ENABLED environment variable format in the docker/external-node.yml file to ensure it is enclosed in quotes.

Detailed summary

• Changed the format of EN_PRUNING_ENABLED from ${EN_PRUNING_ENABLED:-true} to "${EN_PRUNING_ENABLED:-true}" in docker/external-node.yml.

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