fix: neutralize scaffold presets and agent aliases

[bntvllnt]

Summary

• rename the public internal preset to OSS-neutral admin while retaining internal as a deprecated compatibility alias
• remove default .cursorrules / .windsurfrules template emission so generated apps and the npm tarball only ship canonical AGENTS.md and CLAUDE.md
• replace TODO slug-page templates with explicit notFound() placeholders and strengthen scaffold tests for unreplaced placeholders and policy-sensitive markers across every preset
• align README, CLI docs/help, llms files, website copy, tests, and changelog references with canonical naming

Validation

• pnpm test — 150/150 passed
• pnpm typecheck — passed
• pnpm lint — passed
• pnpm build — passed
• pnpm pack --pack-destination /tmp/create-vllnt-app-pack — passed
• packed tarball inspection: alias files .cursorrules / .windsurfrules = 0, canonical agent files AGENTS.md / CLAUDE.md = 6

Notes

• No publish/release performed.
• Next.js build still reports the pre-existing middleware-to-proxy deprecation warning.