[codex] Autosave traffic report schedule controls

[tyemirov]

Summary

• Move the scheduled report enable switch into the traffic reports title bar and remove the manual save button.
• Autosave schedule enablement, frequency, send time, weekday, and month day changes from the dashboard.
• Make recipient and timezone display-only in the UI; recipient is derived from the authenticated user on the API side, and timezone is detected from the browser session.

Validation

• go test ./internal/api -run 'TestGetTrafficReportScheduleReturnsDefaults|TestSaveTrafficReportSchedulePersistsValues|TestSaveTrafficReportScheduleResetsRetryState|TestSaveTrafficReportScheduleRejectsInvalidValues'
• npm --prefix tests run typecheck
• make test-unit
• make lint
• targeted Playwright: npm exec -- playwright test -c playwright.ui.config.js specs/dashboard-traffic.spec.js -g "traffic report schedule can be configured from dashboard" against a fresh temporary integration stack