test: cover template literal concatenation minification

[vercel-gh-bot-3]

Summary

Adds a focused unit regression test for template-literal concatenation during SWC minification. The test uses the public minify() binding with the validated trigger—two interpolated template literals followed by a dynamic suffix—and asserts that the left template's trailing LTAIL> quasi remains in the folded output.

This is test-only and does not include a product fix.

Issue: vercel#95900

Validated behavior

The reporter reproduction was validated unchanged at dd667193b811bfe8a9942da299ddeba441e00f3d:

• Next.js 16.2.10 emitted export function f(o){return"A640B400<r 640RTAIL>"+o}, dropping LTAIL>.
• Next.js 16.3.0-canary.94 emitted export function f(o){return"A640B400LTAIL><r 640RTAIL>"+o}, preserving it.

The test copies that exact minifier input and checks the missing boundary directly.

Validation

pnpm build --filter=next
pnpm jest test/unit/next-swc.test.ts --runInBand
pnpm prettier --check test/unit/next-swc.test.ts
pnpm eslint --config eslint.cli.config.mjs test/unit/next-swc.test.ts

The focused Jest run passed all 4 tests (including the new minifier case), with 2 snapshots.

Base snapshot

The fork base contains the source tree from upstream canary at 89c94877667f1692ae979cc553bf86c763b0a6b0; only the fork's existing .github/workflows/build_reusable.yml is retained because the publishing token cannot update workflow files.