feat(ui): default telemetry off, BYOK-first AI panel

[keshav-k3]

Summary

• Default telemetry:enabled to false for new Termon installs
• Remove the AI panel telemetry hard wall; show a compact cloud-mode notice instead
• On first AI open without custom modes, surface a prominent BYOK setup prompt with highlighted mode selector
• Disable chat input until a valid custom mode is configured or telemetry is enabled for cloud modes

Test plan

• Fresh profile: open AI panel — see BYOK setup welcome, pulsing mode dropdown, telemetry notice banner (not full-screen gate)
• Configure a custom AI mode in waveai.json — panel becomes usable without enabling telemetry
• Enable telemetry — cloud waveai@ modes unlock in dropdown; notice can be dismissed implicitly
• Attempt send without valid mode — input disabled with "Configure an AI mode..." placeholder
• npm run test:unit -- frontend/app/aipanel passes