feat(nextjs): point invalid-key errors at the Clerk CLI

[djgould]

Description

Stacked on #9481. Extends CLI-first error messaging to invalid (fabricated or mistyped) keys, which previously surfaced as a bare Publishable key not valid. with no guidance:

• @clerk/shared: the default invalid publishableKey message now recommends npx clerk@latest init and warns against placeholder keys.
• @clerk/nextjs: clerkMiddleware() validates the publishable key format upfront. Development throws code=invalid_env_keys pointing at npx clerk@latest init; production throws code=invalid_env_keys_production pointing at npx clerk@latest env pull --instance prod.

Sandbox agent trials showed fabricated placeholder keys are the most common agent failure mode, so both messages state the CLI is non-interactive and that invented keys will fail.

Checklist

• pnpm test runs as expected.
• pnpm build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🌟 New feature

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 73ea40f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 23 packages

Name	Type
@clerk/shared	Patch
@clerk/nextjs	Patch
@clerk/astro	Patch
@clerk/backend	Patch
@clerk/chrome-extension	Patch
@clerk/clerk-js	Patch
@clerk/electron	Patch
@clerk/expo-passkeys	Patch
@clerk/expo	Patch
@clerk/express	Patch
@clerk/fastify	Patch
@clerk/headless	Patch
@clerk/hono	Patch
@clerk/localizations	Patch
@clerk/msw	Patch
@clerk/nuxt	Patch
@clerk/react-router	Patch
@clerk/react	Patch
@clerk/tanstack-react-start	Patch
@clerk/testing	Patch
@clerk/ui	Patch
@clerk/vue	Patch
@clerk/swingset	Patch

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Project	Deployment	Actions	Updated (UTC)
clerk-js-sandbox	Ready	Preview	Aug 18, 2026 5:47pm
swingset	Ready	Preview	Aug 18, 2026 5:47pm

[djgould]

Superseded by #9486 — restacked fresh off main as part 3 of the keyless→CLI stack (#9484 → #9485 → #9486).