Prepare mobile app store launch

[ejones23]

Summary

• add a public privacy-policy page plus an accessible native Privacy & support screen
• declare production/staging universal and app links while keeping development unassociated
• add non-deployable Apple and Android association templates with placeholder-safety tests
• document verified iOS setup and the end-to-end store release, rollout, and rollback gates
• update the Expo RFC with completed Android/iOS verification and remaining launch prerequisites

Safety and scope

The association templates deliberately remain outside the deployable web tree. They require the final Apple Team ID and Google Play app-signing fingerprint. This PR does not register store identities, publish association files, deploy APIs, upload builds, or authorize a public release. The maintainer must review the privacy language against actual operating practices before deployment.

Verification

• npm test: 191 Vitest tests and 231 PHPUnit tests / 587 assertions passed
• npm run build passed; privacy-policy.html copied into dist
• npm run test:e2e: all 3 Playwright browser flows passed
• mobile: 69 Vitest tests, TypeScript, Expo lint, and static web export passed
• resolved Expo configs checked for development, staging, and production identities/link declarations
• Xcode MCP build passed with zero errors on Xcode 26.6 / iOS 26.5 simulator
• simulator rendered and navigated the new accessible Privacy & support screen

Known launch blockers

• production API v2 ballot/vote endpoints are not deployed
• rankedchoices.com association files are not published
• durable store-account ownership, Apple Team ID, and Play signing fingerprint are not final
• staging, signed physical-device testing, privacy review, TestFlight, and Play internal testing remain release gates