Fix Helm chart values for environment-specific configuration

[Wilfred007]

What

Helm chart has values.yaml and values-production.yaml but missing staging values. Resource limits and replica counts need per-environment tuning.

Why

Different environments need different resource limits, replica counts, and feature flags. One size doesn't fit all.

Scope

In scope: values-staging.yaml, document all values, resource limits per environment
Out of scope: Helm operator

Acceptance Criteria

• Separate values files per environment
• Resource limits appropriate per environment
• Feature flags configurable per environment
• README documenting all values

Technical Context

• charts/payd/values.yaml — default values
• charts/payd/values-production.yaml — production