[brionmario]

Purpose

Moves the Better Auth Next.js integration sample here from thunder-id/javascript-sdks (samples/integrations/better-auth/nextjs), so every ThunderID sample lives in this repository (thunder-id/thunderid#5904).

Approach

• Location: integrations/better-auth-nextjs, next to integrations/flutter-app-auth, copied from the tracked files only.
• Published package: depends on the published @thunderid/better-auth 0.1.1 instead of workspace:*, so it runs on its own. prepare-dev.cjs no longer rewrites workspace dependencies, since there are none.
• Standalone install: has its own pnpm-lock.yaml and .gitignore, plus the postcss override that the Next.js quickstart carries for the next-bundled postcss advisories, with the same justification.
• README: the StackBlitz badge points here, the @thunderid/better-auth link is now absolute, and setup gains a pnpm install step (previously the monorepo root install covered it).
• CI and release: the PR builder already discovers integrations/<name>/package.json. The release workflow gains a sample_better_auth_nextjs input, and the root README lists the sample.

Verified locally: pnpm install --frozen-lockfile, pnpm audit --audit-level=high (no known vulnerabilities), and pnpm build, with and without a .env, against the published package.

Related Issues

• Move the SDK quickstart samples to the thunder-id/samples repository thunderid#5904

Related PRs

• Move the samples to the samples repository and add playgrounds javascript-sdks#126 (removes the sample from the SDK repository)
• Point the docs at the samples repository and document the SDK playgrounds thunderid#5910 (repoints the docs)
• Stop concurrent sample releases from failing on push races #8 (release workflow push race; touches the same workflow)

Merge order: this PR before thunder-id/javascript-sdks#126 and thunder-id/thunderid#5910.

Checklist

• Followed the contribution guidelines.
• Manual test round performed and verified.
• Documentation provided. (Add links if there are any)
• Tests provided. (Add links if there are any)
  • Unit Tests
  • Integration Tests
• Breaking changes. (Fill if applicable)
  • Breaking changes section filled.
  • breaking change label added.

Security checks

• Followed secure coding standards.
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.

[brionmario]

Combined into #11 together with the other sample changes, one commit each.