Show uNotch in link previews and refresh the side-notch logo

[SethMed7]

What and why

Shared links currently show only the wallpaper. Replace that image with a versioned 1200 × 630 PNG showing the tagline, provider names, and the site's usage HUD, and set matching Open Graph and Twitter metadata.

Replace the U-shaped logo with a rounded screen and an inset side notch across the SVGs, favicons, app icon generator, menu bar, and settings. Keep editable sources and generation scripts for both the card and web icons, and update the brand documentation.

Checklist

• swift test is green locally (20 tests)
• No product behavior changes; existing render tests pass
• No new runtime dependencies, telemetry, or network calls
• UI changes follow the existing palette and updated brand mark
• CHANGELOG.md includes the changes under Unreleased
• Desktop and mobile checked; settings demo opens and closes correctly
• Site assembly succeeds; image metadata matches the PNG dimensions; local crawler requests return HTTP 200 and image/png

Screenshots