feat(webui): use nextjs middleware to dynamically redirect API calls

[PragmaTwice]

This includes:

• update nextjs from 14 to 15
• remove the URL rewrite function from next config
• add a nextjs nodejs middleware to rewrite URLs dynamically (without rebuild the webui!)
• enable standalone mode
• add an env var KVCTL_API_HOST for running node with dynamic endpoint (server side)

[Copilot]

Pull Request Overview

This PR upgrades Next.js from version 14 to 15 and implements dynamic API routing using Next.js middleware instead of static URL rewrites. The changes enable runtime configuration of API endpoints without requiring webui rebuilds.

• Update Next.js from 14.2.29 to 15.5.4 and React from 18 to 19
• Replace static URL rewrites in next.config.mjs with dynamic middleware-based routing
• Implement standalone build mode for containerized deployments

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
webui/package.json	Updates Next.js and React versions, adds deployment script
webui/next.config.mjs	Removes static API rewrites, enables standalone mode
webui/src/middleware.ts	Adds middleware for dynamic API routing using KVCTL_API_HOST
webui/tsconfig.json	Formatting improvements and target specification
webui/src/app/page.tsx	Fixes useRef initialization for React 19 compatibility
webui/src/app/namespaces/[namespace]/page.tsx	Updates params handling for Next.js 15 async params
webui/src/app/namespaces/[namespace]/clusters/[cluster]/page.tsx	Updates params handling for Next.js 15 async params
webui/src/app/namespaces/[namespace]/clusters/[cluster]/shards/[shard]/page.tsx	Updates params handling for Next.js 15 async params
webui/src/app/namespaces/[namespace]/clusters/[cluster]/shards/[shard]/nodes/[node]/page.tsx	Updates params handling for Next.js 15 async params

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[Copilot]

The matcher pattern only covers /api/v1 but the middleware function checks for url.pathname.startsWith('/api/v1'). Consider aligning these patterns or using a more specific matcher like '/api/v1/:path*' to ensure consistency.