refactor: standardize helm charts and release flow

[jlon]

Summary

• standardize the Helm repo structure, install docs, and published chart naming around GitHub Releases plus the public curvine-doc index
• add schema validation for both charts, simplify runtime defaults, remove the non-standard runtime upgrade hook, and fix CSI/runtime chart template and values issues
• harden the release workflow so only version tags can sync the public index, release metadata resolves the real source SHA, and the default runtime chart now passes helm lint/template

Test Plan

• git diff --check
• helm lint ./curvine-runtime
• helm template curvine ./curvine-runtime
• helm template curvine ./curvine-runtime -f ./curvine-runtime/examples/values-dev.yaml
• helm template curvine ./curvine-runtime -f ./curvine-runtime/examples/values-prod.yaml
• helm template curvine ./curvine-runtime -f ./curvine-runtime/examples/values-baremetal.yaml
• helm lint ./curvine-csi
• helm template curvine-csi ./curvine-csi
• actionlint .github/workflows/release.yml
• YAML/JSON schema parsing for workflow, values, examples, and chart schemas