Establish trusted voter guide Gate 0

[uncomposed]

What changed

• adds the trusted voter-guide product constitution and pre-pivot evidence baseline
• pins Node 20 and adds CI for lint, unit tests, and production build
• makes the legacy Playwright server precondition explicit while recording the retired-product failures Gate 1 will replace

Why

This creates an auditable preservation and quality boundary before replacing the multi-tool workspace with the trusted voter-guide MVP.

Validation

• npm run lint (legacy warnings only)
• npm run test:run (32 passed)
• npm run build
• configured Playwright run exposed and documented two legacy failures; Gate 1 replaces those tests before deployment