fix(cli): adapt to shadcn template drift breaking TanStack Start and Next.js scaffolds

[envindavsorg]

Problem

bun create tauri-ui currently fails for two of the five templates because the upstream shadcn templates changed shape:

TanStack Start — scaffolding always aborts with:

▲  Scaffolding failed
└  Could not mount ExternalLinkGuard in the TanStack Start root route.

The generated src/routes/__root.tsx now ships a notFoundComponent containing its own <main className="container mx-auto p-4 pt-16">, declared before RootDocument. The scroll-container battery's "upgrade an existing <main>" regex matched the first <main> in the file, so it tagged the 404 page's element with data-ui-scroll-container instead of wrapping {children}. The external-link-guard battery then couldn't find <main…>{children}</main> and threw, aborting the whole scaffold.

Next.js — scaffolding aborts with ENOENT: no such file or directory, open '…/next.config.mjs'. The template now generates a typed next.config.ts (const nextConfig: NextConfig = {}) and a plain "dev": "next dev" script without --turbopack, so the static-export patch crashed and the -p 1420 port rewrite silently no-opped.

Fix

• batteries/scroll-container.ts: the upgrade path now only targets a <main> that directly wraps the route content ({children}, <App />, <Outlet />, <slot />) via a lookahead anchor passed per template, leaving unrelated <main> elements (like the Start 404 page) untouched. Also hardened the idempotency check so a previously upgraded <main> carrying extra attributes is still detected.
• adapters/next.ts: resolves next.config.ts/.mjs/.js (first match), patches both the typed and untyped empty-config shapes, and appends -p 1420 to any next dev script that doesn't already pin a port.

Verification

• Reproduced the original failure with --template start before the fix.
• After the fix, the exact failing invocation (--template start --no-starter --size-optimize --workflow) scaffolds successfully and the generated app passes bun install && bun run build.
• Full simple test matrix (node scripts/test-create-tauri-ui-simple.mjs) passes for all five templates:

- PASS vite (14.5s)
- PASS next (20.2s)
- PASS start (15.4s)
- PASS react-router (15.2s)
- PASS astro (18.4s)

• oxlint / oxfmt --check / tsc --noEmit clean (the single pre-existing libRoot warning on master is untouched).
• Changeset included (patch bump for create-tauri-ui).

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[anton-liam]

when will merge it, i cant create project with nextjs template