ci: unblock dependency PR checks - #26

Summary

• make dependency-review non-blocking when repository dependency graph is disabled
• configure golangci-lint action to report only new issues in PRs
• switch frontend install to npm install and remove lockfile-dependent npm cache setup

Why

Current Dependabot PRs fail before dependency updates can be validated due repo-level CI configuration constraints unrelated to the dependency diffs.

Validation

• Ran frontend quality flow in a clean archived checkout (no untracked files): lint, vitest, and next build all passed.
• Confirmed backend tests still pass locally via go test ./...