Add private Founder Beta acquisition funnel

[fly1d]

Summary

• replace the public GitHub Issue waitlist with a private bilingual Tally form
• preserve validated campaign sources through the landing page and record page language separately
• disclose coarse funnel metadata, Tally processing, and enforce explicit retention limits
• publish a separate privacy request form for access, correction, and deletion
• keep GitHub issue templates as optional public feedback paths

Review fixes

• preserve inbound DEV and Hashnode attribution instead of collapsing all traffic to product-page
• cap undecided application retention at 90 days
• make the Tally eligibility and privacy copy bilingual
• disclose hidden source and language fields
• document weekly external-form contract checks without creating fake submissions

Verification

• npm run check
• npm run test:smoke
• npm run test:site
• npm run desktop:check
• node --check site/waitlist.js
• desktop and 390px mobile screenshots for Chinese and English
• public waitlist and privacy forms returned HTTP 200 and matched the documented field contract