refactor: NextJS to vite/react-router

[Vbsof]

Issue #, if available:

Description of changes:
Refactor NextJS frontend to less opinionated Vite based build.

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[brianz]

Thank you for this contribution @Vbsof ! I was able to deploy it successfully, and there isn't a single Typescript error or warning...looks great. I like the addition of tests.

Only a few comments:

• Let's keep the "use client" declarations, especially in the shadcn components. There isn't any harm in leaving those that I'm aware of, and sets up future builders for success if they move to SSR.
• One test/spec fails now: should copy public assets to build directory. Look like this is because of the removal of favicon.
• There are a couple of references to "next.js" still, which is non-functional text, but we should still clean that up:

rg -i "next\.js"
CHANGELOG.md
75:- **CRITICAL**: Updated React to 19.2.1 and Next.js to 16.0.7 to address CVE-2025-55182 (CVSS 10.0)
112:- Full-stack React frontend with Next.js, TypeScript, and Tailwind CSS

scripts/deploy-frontend.py
8:Deploys the Next.js frontend to AWS Amplify by:
478:    log_info("Building Next.js app...")

infra-cdk/lib/amplify-hosting-stack.ts
87:      description: `${props.config.stack_name_base} - React/Next.js Frontend`,

• Please update the Changelog to document removal of next.

[Vbsof]

Hello @brianz thank for the review.

I have made the changes you requested. For the failing test i have removed the path test. It's a little overkill i feel. Many of the tests was added to make sure the migration worked after all the changes.

I think the PR should be ready to merge now! :)

Vetle