Add privacy-preserving analytics funnel

[Sikkra]

Summary

• add a Do-Not-Track-aware Plausible manual analytics wrapper for app funnel events
• track coarse funnel steps: landing view, launch/demo clicks, app load, successful wallet connect, and submitted deposit flows
• keep analytics props free of wallet addresses, emails, transaction hashes, exact amounts, and free-form user input
• add a landing privacy page documenting cookie-free analytics, tracked fields, and DNT behavior

Closes #98

Verification

• npm run build (frontend)
• Playwright/Edge smoke: landing loads Plausible manual script and queues Landing Viewed, Launch App click queues with target=hero, DNT context loads no analytics script and no plausible queue, app queues App Loaded without wallet/PII/amount-like props, privacy page screenshot captured
• git diff --check