feat(adapters): persist generated GitHub App keys

[Railly]

Summary

• generate omitted GitHub App private keys in the Next.js and Nuxt adapters
• persist and restore one canonical identity across cold starts and concurrent instances
• expose generated keys only through the server-side generatedSecrets() accessor
• publish file snapshots atomically and preserve explicit-key and legacy-snapshot compatibility
• document the complete embedded adapter workflow

Verification

• pnpm build
• pnpm type-check
• pnpm test
• pnpm lint
• pnpm format:check
• git diff --check
• Test Strength: ten critical mutations killed; failed-save cleanup and HTTP header/body non-exposure coverage strengthened
• Resilience Audit: ambiguous initialize/save success, transient load, malformed canonical state, save-queue recovery, and eight-way cold starts forced
• pressure repetition: 10 rounds, 140 Next cases, 140 Nuxt cases, and 760 core cases without flakes
• final Cursor Grok 4.6 xhigh review: zero actionable findings

Part of #203. This completes Slice 3; merge and release remain maintainer-controlled.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
emulate	Ready	Preview, v0	Aug 25, 2026 10:14pm