fix(e2e): validate rendered server fixture

[vishr]

Summary

• restore valid quoted Go-template scalars for the real-server target and backup endpoint
• normalize the remaining backup enum values to the v1alpha1 contract
• render and load the server fixture in the ordinary test suite so malformed templates fail before release E2E

Verification

• go test ./e2e -run TestPostgresServerFixtureRendersValidApplication -count=1
• just check

Release context

Release v2026.9.12 reached GitHub Actions but did not publish artifacts because both real-server shards rejected the malformed rendered YAML. This fixes that release gate; the next release revision will be used after merge.