style: onboarding title/font polish + 8-bit dark/light theme matching

[torrmal]

Summary

Visual polish on the onboarding screens and the 8-bit skin, layered on top of the merged SSO-first onboarding (#184).

Onboarding titles & welcome

• Welcome-orb caption and screen titles now match the app's hero greeting ("Let's knock something off your list") — var(--font-display), 36px / 700 / -0.02em, sentence case.
• Titles are sentence-case strings; arcade mode re-uppercases via CSS so the retro look is preserved while normal mode reads like the app.
• First loading/welcome screen now renders on the app's actual window background for the current theme/skin (instead of the arcade backdrop), with the CRT overlay dropped.

8-bit dark mode

• App-wide background now uses the sign-in screen's arcade backdrop (#0a0a13 base + soft top glow + heavier scanlines & vignette), applied via the body so the main app, sidebar, and loading screen all share one consistent effect.
• Gravity-field "gravitational dots" hidden in 8-bit dark.
• Sidebar + input/panel surfaces restored to the arcade card/edge tones so they harmonize with the background.
• Softened the text ink ramp (top ink #ecedf6 → #d4d5d9) so fonts aren't glaring white.
• Sidebar cyan halo dialed down.

8-bit light mode

• (Left as the Game Boy green palette per design.)

Test plan

• Switch skin (arcade ↔ normal) via the corner gamepad on onboarding.
• Toggle 8-bit / dark / light in the in-app Display modal and verify backgrounds, inputs, sidebar, and text contrast.

🤖 Generated with Claude Code