[User Story] Update ghost-compose.service working directory

[noahwhite]

Story Summary

As a platform engineer, I want to update the ghost-compose.service systemd unit to use the new ephemeral config location, so that Docker Compose runs from /etc/ghost-compose/ instead of block storage.

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✅ Acceptance Criteria

• WorkingDirectory changed from /var/mnt/storage/ghost-compose to /etc/ghost-compose
• Service still depends on docker.service and var-mnt-storage.mount
• Service unit file syntax valid

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📝 Additional Context

• Design: The service still requires var-mnt-storage.mount because .env.secrets is on block storage
• No other changes needed to the service file

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📦 Definition of Ready

• Acceptance criteria defined
• No unresolved external dependencies
• Story is estimated
• Team has necessary skills and access
• Priority is clear
• Business value understood

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✅ Definition of Done

• All acceptance criteria met
• Peer-reviewed
• Systemd unit syntax valid

[linear]

GHO-48