fix(helm): refresh OpenViking chart defaults

[ZaynJarvis]

Summary

• default the Helm chart to ghcr.io/volcengine/openviking:latest and decouple image selection from Chart.appVersion
• document latest / main / pinned tags such as v0.3.17; an empty image.tag also falls back to latest
• align Kubernetes deployment with the current Docker image layout by using /app/.openviking/ov.conf, the image entrypoint, and OPENVIKING_WITH_BOT=0 by default
• update persistence defaults/docs and secret-based API key examples so the Service still exposes only port 1933

Validation

• helm lint deploy/helm/openviking
• helm template openviking deploy/helm/openviking --namespace default
• helm template openviking deploy/helm/openviking --namespace default --set image.tag= renders ghcr.io/volcengine/openviking:latest
• git diff --check
• deployed with helm upgrade --install openviking ./deploy/helm/openviking --namespace default --set image.tag=main ... --wait --timeout 10m
• verified kubectl get svc shows ClusterIP with only 1933/TCP
• verified local port-forward 127.0.0.1:1933 -> svc/openviking:1933, /health, /ready, and authenticated /api/v1/system/status
• verified installed ov CLI can connect via a temporary ovcli.conf, read/write viking://resources/helm-smoke/cli-20260522T071348Z.md, and retrieve it with ov find
• verified workspace persistence by restarting deployment/openviking, then reading and finding the same smoke-test resource after the new pod became Ready

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[t0saki]

LGTM