Track expense input exploration

[PengfanZ]

Summary

• track deliberate switches between manual, AI text, and AI voice expense input tabs
• preserve privacy by sending only allowlisted event, surface, locale, and anonymous session data
• add the Supabase event allowlist migration and explorer-session reporting
• document the explorer → request → outcome funnel

Verification

• 574 unit/component tests with 100% coverage
• lint, typecheck, and production build
• 14 standard and 14 AI Playwright tests
• rendered local browser QA with no console warnings or errors
• database pgTAP runs in CI because Docker Desktop was unavailable locally