[Enhancement] Simplify Helm Chart Structure - Remove Values Duplication Across All Services

[NotYuSheng]

Description

All 15 Helm services have values.yaml files that are nearly identical copies of values-prestaging.yaml with only minor additions (18-43 line differences). This violates Helm best practices, creates unnecessary complexity, and makes configuration management time-consuming and error-prone.

Current State:

• Affected Services (15 total): chat-service, embedder-service, pdf-processor-service, docling-translation-service, metadata-service, image-captioner-service, pdf-extraction-service, pdf-renderer-service, frontend, cleaner, chromadb, minio, nginx, redis, istio-gateway
• Line Differences: Range from 18-43 lines between values.yaml and values-prestaging.yaml
• Impact: Unclear what actually differs between environments, maintenance overhead, violates Helm chart best practices

Technical Problem:
The current approach duplicates prestaging-specific configurations as defaults, making charts unnecessarily complex. This pattern emerged across all services and needs architectural simplification.

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Acceptance Criteria

1. The task is complete when Helm chart structure is simplified and duplication is eliminated.
2. Additional requirement: Environment-specific configurations are clearly separated from defaults.

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Notes

• This is an architectural issue affecting the entire project's infrastructure
• Current complexity makes configuration time-consuming and error-prone
• Consider broader Helm chart simplification as mentioned in project discussions
• RBAC service was the only one that didn't follow this duplication pattern initially