feat(paperless-gpt): add chart

[fty4]

Summary

• add paperless-gpt chart using the official upstream image icereed/paperless-gpt (default tag v0.29.0)
• Deployment (1 replica, Recreate, SQLite state), ClusterIP Service, PVC for /app/{prompts,config,db}, Secret
• provider-agnostic config via config, secretConfig and existingSecret; paperless API token via value or existing secret
• runs non-root (10001), capabilities dropped; TCP probes (no documented upstream health endpoint)
• add chart to the README table

Notes

• upstream has no authentication: only a ClusterIP service is created, ingress must sit behind an authenticating proxy
• ct install may fail in CI if the app exits without a reachable paperless-ngx; if so, add the chart to --excluded-charts

Test plan

• helm lint with ci/ct-values.yaml
• ct lint --check-version-increment=false --target-branch main
• helm template with inline and existing secrets, and failure without a token
• CI ct install in kind