fix: keep release metadata checks version-agnostic

[ernescz]

Summary

• repair the three normal main-branch checks exposed by the first coordinated app/chart release
• update both visible Helm README badge labels and badge URLs during release preparation
• make release-contract fixtures derive future versions from current metadata and control their own Unreleased sections
• verify the default image against an injected Chart appVersion instead of a released version constant
• pin helm-docs to v1.14.2 so generated README formatting is reproducible

Verification

• reproduced the release-contract collision on chart 0.1.1 and the Helm image expectation mismatch
• regression test failed before the badge-label generator fix and passed afterward
• bash scripts/tests/release-scripts-test.sh (11/11)
• Helm 3.16.4 + helm-unittest 0.5.2 (37/37)
• helm-docs v1.14.2 regenerated README byte-for-byte
• Helm lint and render smoke test
• go test -race -count=1 ./...
• go build ./...
• go vet ./...
• golangci-lint run ./... (0 issues)
• gosec -quiet ./...
• task docs:validate
• independent review: no Critical, Important, or Minor findings after follow-up

Checklist

• Tests were added or updated where behavior changed.
• Documentation was updated where user-facing behavior changed.
• CHANGELOG.md was updated for a notable user-facing change.
• Every commit includes a DCO Signed-off-by trailer.