feat: propagate referrer through the download flow for referral attribution

[braianj]

Carries the invite referrer through the full download flow so the installer chain can attribute the referral, behind the INVITE_DIRECT_DOWNLOAD configuration gate (off in prod).

• Invite CTA goes directly to /download with the referrer on desktop when the gate is on; mobile keeps the auth-login-first flow.
• The referrer is appended to the gateway file URL in both DownloadOptions and DownloadSuccess (the real download trigger), and a referrer forces the anonymous gateway route so the CDN fallback can't drop it.
• Session-persisted on the invite page (set-or-clear) so it survives navigation without reusing a stale attribution.

Verified: full suite green (3521 tests), lint, typecheck and build pass.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
sites	Ready	Preview, Comment	Jul 27, 2026 2:38pm

[coveralls]

Coverage Report for CI Build 30275962172

Coverage decreased (-0.004%) to 96.112%

Details

• Coverage decreased (-0.004%) from the base build.
• Patch coverage: 1 uncovered change across 1 file (46 of 47 lines covered, 97.87%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
src/utils/referrer.ts	24	23	95.83%
Total (7 files)	47	46	97.87%

Coverage Regressions

No coverage regressions found.

---

Coverage Stats

Relevant Lines:	10480
Covered Lines:	10394
Line Coverage:	99.18%
Relevant Branches:	4850
Covered Branches:	4340
Branch Coverage:	89.48%
Branches in Coverage %:	Yes
Coverage Strength:	17.78 hits per line

---

💛 - Coveralls