Add commented examples for optional environment variables in docker-compose.prod.yml

[duplico]

Context

Follow-up from PR #424 review (comment 2748040667).

Issue

The README.md documents setting MAGPIE_TLS_CONFIG for manual TLS certificates, but docker-compose.prod.yml doesn't include this as a commented-out example. This makes the feature less discoverable.

Recommended Fix

Add commented-out examples for optional configuration:

• MAGPIE_TLS_CONFIG for manual TLS certificates
• Any other optional production settings

Acceptance Criteria

• Add commented examples for optional env vars in docker-compose.prod.yml
• Ensure examples match README documentation

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Created from PR #424 review feedback.
(AI-generated via Claude Code w/ Opus 4.5)