provider:vercel - Add example for env var mismatch between preview and prod

[ohad6k]

Contributor path

Provider mapper

What

Add examples/provider-drift/vercel-env-mismatch.md showing NEXT_PUBLIC_* (or another env var) differing between Vercel preview and production, how VibeRaven surfaces the drift, and the fix.

Why

Env var drift between preview and prod is a top cause of "works in preview, breaks in production" for AI-built apps.

Acceptance criteria

• File shows both environments (preview vs. production) with the differing value (redacted)
• Shows the VibeRaven finding text
• Shows the agent next-action + the Vercel dashboard step

Effort

~30–90 minutes