feat(marketing): add a nightly channel to the download page

[t3dotgg]

The site never mentioned nightly builds. Nightly ships several times a day to GitHub prereleases and npm, but the only way to find one was the raw releases page.

The download page gets a Stable / Nightly toggle. Nightly reads the newest prerelease from the GitHub releases list in the browser, so the site does not need a rebuild to show a new build. The nightly channel swaps in the nightly app icon and the DMG sky art. The nav gets a Download text link so the full download list is one click from every page.

/download?channel=nightly is a shareable link that opens on the nightly channel.

Before

Home

Download

After

Home. The only change is the Download link in the nav.

Download, stable

Download, nightly

Notes

• Both channel icons stay mounted and cross-fade, so the title and cards never shift.
• The sky is a static SVG cut from apps/desktop/resources/dmg/dmg-background-nightly.svg with the text and cursor removed. It fades in on toggle and masks out at the bottom. No continuous animation.
• The mobile section hides on nightly, since there is no nightly mobile build. A Terminal section with npx t3@nightly shows instead.

Created with Claude Fable 5.1 in Claude Code.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+5 B (+0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−6 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+11 B (+0.2%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	−8 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	−8 B (−0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 7ac93e3 · PR result: 20d2872 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.