fix(frontend): enforce supported Node runtime

[anirudh5harma]

Summary

Frontend installs now reject unsupported Node runtimes before npm creates node_modules, preventing the partial Electron installation reported in #2206. Local setup and every desktop/frontend workflow use Node 24, which is the current supported LTS line and satisfies the frontend dependency engine requirements.

This is a contributor-development guardrail, not an end-user launch fix. ao start opens the released Electron app and its bundled daemon without using local frontend dependencies; npm run dev is needed only when running the Electron frontend and Go daemon from source so local changes are exercised together.

This supersedes the initial lifecycle-hook implementation in this PR: validation showed that npm runs Electron's dependency postinstall before the root package's preinstall, so that hook could still leave Electron incomplete. The enforced engines contract with engine-strict performs the check before dependency installation instead.

This ports the intent of aoagents/ReverbCode#413 onto the canonical repository with the install-order issue corrected.

Validation

• Node 26: npm ci exits with EBADENGINE and does not create node_modules.
• Node 24: clean npm ci completes and Electron's binary/path marker is present.
• npm run typecheck
• npm test -- --run (40 files, 370 tests)
• npm run package
• npx @redwoodjs/agent-ci run --workflow .github/workflows/frontend.yml (1 job passed)
• Prettier and git diff --check

Post-Deploy Monitoring & Validation

Watch the first frontend, nightly, testing-build, and release workflows after merge. Healthy behavior is a clean Node 24 install followed by the existing test or packaging steps on each runner; an engine rejection or cross-platform packaging regression is the rollback trigger.