Design decisions surfaced during review of PR #6910 and #6942 that need team alignment before the design doc is finalized.

• "daily" vs "nightly" channel naming — Industry convention uses "nightly" (Rust, Firefox, Chrome). Our builds are per-commit to main, not nightly schedules. Keep "daily" or rename to "nightly"?
• MSI for script-install updates on Windows — Current implementation uses MSI for all non-package-manager Windows installs, which escalates privileges beyond the original install-azd.ps1 install. Use binary replacement for script installs instead? Related to azd update: leverage existing install scripts for download and verification #6987.
• Config convenience flags on azd update — Keep --auto-update and --check-interval-hours flags on the command (convenience), or require azd config set for all config changes (separation of concerns)?
• "update" vs "upgrade" command name — azd extension upgrade uses "upgrade". Package managers use "upgrade". hemarina: consistency. kristenwomack: "update" is industry standard for self-update.
• Background download consent model — Auto-update (with background download) defaults off, alpha-gated, CI-skipped. Is opt-in background download acceptable, or should it be check-only + banner permanently?

Context: Design doc PR #6910, Implementation PR #6942, Epic #6721

Once decisions are made, design doc will be updated accordingly.