Settings and first-run onboarding: display (mode, overscan, HDR), audio (device, channels, passthrough), network (Ethernet/Wi-Fi status, hostname), sources & libraries, remotes (CEC/BT/IR pairing), screensaver, updates, about/diagnostics

Epic: #113 · Milestone: MC7 — TV shell

Tasks

• Onboarding wizard on first boot: language, display check (pattern + "can you see this?" with auto-revert), audio test tone per channel, network status, add first source, remote pairing, done.
• Settings screens as .stx, backed by the settings store; every setting has a default, a validator, and takes effect without reboot where possible.
• Diagnostics: serial log viewer, perf numbers, network test, storage health, "report bug" QR (via qrx-style encoder ported to Home) linking to a support page with the device log ID.
• Updates: channel selection, check/apply/rollback UI over #109.
• Factory reset (keeps or wipes library) over #110.

Acceptance

Golden frames; scripted onboarding test completes in QEMU; settings persist across reboot on the Pi.

Size: M · Depends on: #92 · Blocks: v1