fix: repair Helm release upgrade flow

[bugkeep]

Summary

• route Helm release upgrades through a dedicated SSE endpoint backed by action.NewUpgrade
• preserve new chart defaults while reusing prior user overrides with ResetThenReuseValues
• persist credential-free chart repository identity so existing releases can locate their chart repository during later upgrades
• reload chart values when a legacy release is given its missing repository URL
• restore diagnostic details for callers of the non-streaming upgrade endpoint
• restore background upgrade tasks by exact chart, namespace, release, and operation identity
• return exact chart name and version fields while retaining the legacy combined chart field for compatibility
• add English and Chinese translations for the upgrade flow and remove superseded installation-only keys

Why

The Helm Releases page previously opened the install flow with an empty repository URL. The backend then attempted to fetch /index.yaml without a URL scheme, so releases could not be upgraded from this page.

Verification

• go test ./... -tags skipCi -count=1
• cd web && CI=true yarn react-scripts test --watchAll=false --runInBand (22 tests)
• cd web && yarn run build
• local regression verified that entering a repository URL for a legacy release reloads its values without allowing an older chart response to overwrite them
• manually upgraded casos-test-nginx in the in-app browser: revision advanced from #2 to #3, remained deployed, and the repository URL stayed prefilled for the next upgrade