chore: scaffold Next.js 16 admin app with ITA ITO design tokens

Set up the project skeleton for the ITA ITO opening-hours display admin:
Next.js 16 (App Router) with TypeScript in strict mode, Tailwind CSS 4,
Vitest, ESLint and a blocking CI workflow.

The design tokens are copied verbatim from the model_ita_ito project
(palette, Inter Variable + Source Serif 4, radii, dark theme) so the two
applications look like one family, as required by the spec.

ESLint is pinned to v9: eslint-config-next bundles a react plugin that
crashes on ESLint 10. The typed `consistent-type-imports` rule is left
out because `verbatimModuleSyntax` already enforces the same discipline
at compile time, without the cost of typed linting across the repo.

PLAN.md records the agreed architecture, including the decisions that
depart from the original spec — most importantly the move from BYOD to
a self-hosted BYOS server, which removes the TRMNL private plugin, the
Liquid template and the webhook entirely.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012cSY9pVhZmJUKNN7wf1Myd

LICENSE

@@ -0,0 +1,7 @@
+Copyright (c) 2026 ITA ITO. All rights reserved.
+
+This software is proprietary and confidential. No part of it may be copied,
+modified, distributed, sublicensed or used, in whole or in part, without the
+prior written permission of the copyright holder.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND.