feat: migrate management UI to Next.js

[cluic]

What changed

Migrate the complete local management UI to a deterministic Next.js App Router static export using React, Tailwind CSS, shadcn source components backed by Base UI, and Lucide icons. The existing same-origin Admin API, session/CSRF permissions, routing behavior, and UI contracts remain intact.

The generated package ships the reviewed static route/Flight/chunk set with a private asset manifest and per-document CSP hashes. The build digest fingerprints the UI source and dependency graph while normalizing only package-lock root version fields, so Changesets version-only release PRs remain compatible without rebuilding frontend assets.

Release output is generated from a clean Ubuntu Node 22.19 canonical build. The canonical artifact was reviewed and committed for this PR; macOS, Windows, and Linux validate the committed source digest, manifest, CSP, resource set, and platform behavior.

Validation

• Release Preflight #104: canonical checkout verify, lint, deterministic tests, runtime audit, package-content, and Changeset checks passed.
• Platform Tests #143: canonical Linux UI build passed; Linux and macOS deterministic/native gates passed; Windows deterministic/native gates passed.
• Chromium E2E: macOS 73/73 and Windows 73/73.
• Deterministic test totals: Linux/Windows 680 tests with 13 skipped; macOS 684 tests with 1 skipped.
• Runtime npm audit: 0 vulnerabilities; package-content and release-workflows: 15/15.
• Workflow run: https://github.com/cluic/codex-remote-proxy/actions/runs/34011524610
• Release preflight run: https://github.com/cluic/codex-remote-proxy/actions/runs/34011524607
• Local full npm test remains unable to bind 127.0.0.1:15100 because the user's existing CRP service owns that port; the service was not stopped, and the clean CI serial chain passed.