docs: explain Gatekeeper and immutable preview downloads

[promisepreston]

What changed

• replace the unreliable Control-click-only instructions with the observed macOS Gatekeeper recovery flow
• document Done, System Settings, Privacy & Security, Open Anyway, authentication, and final Open
• retain exact source and checksum verification and prohibit Gatekeeper or quarantine bypasses
• explain that Whisper Small English and IBM Granite 4.1 3B are bundled and selected by default for their respective roles
• explain the measured 2,528,517,650-byte ZIP and recommend at least 6 GB free during download and extraction
• support a manifest-pinned immutable R2 download for the current oversized package while retaining exact historical GitHub assets
• require metadata-only GitHub release notes to name the exact accepted R2 URL
• show large package sizes in GB and preserve browser-local update tracking
• add Markdown, HTML, release-history, and safety regressions

Why

A tester saw only Move to Bin and Done on first launch and succeeded through Privacy & Security and Open Anyway. The next candidate also bundles Granite, so the portal must explain both the safe installation path and why the archive is large. GitHub keeps dated release notes while the immutable RecordCove download domain serves the oversized verified package.

Validation

• npm test passes 14/14
• npm run build passes
• git diff --check passes
• exact head: 26920a4d2aa91aa5ea39e2897c1646d81eaefd75

Protected boundary

This draft does not change the accepted release manifest, upload the archive, or deploy the site. Merging to main triggers the separately governed Cloudflare Pages deployment and therefore remains closed until the application package, publication workflow, and exact manifest transition are accepted together.

[coderabbitai]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud