Add browser coverage for human-readable routes

[snowyukitty]

Type of Change

• Utilities: Normalize Vite module IDs while resolving island entry points.
• Tests: Add route-adjacent Vitest Browser/Playwright coverage for the human-readable API and library-version routes.
• Something else: Install Chromium and run the browser suite in CI.

What issue does this relate to?

Fixes #188

What should this PR do?

• Run browser tests against a real local Worker through Cloudflare's createTestHarness() lifecycle and a same-origin Vite proxy.
• Assert the /api documentation and /libraries/backbone.js/1.1.0 version page when WEBSITE_BASE identifies the website origin.
• Exercise the hydrated Files island by selecting the displayed Source Maps filter and checking the resulting file links.
• Keep browser coverage beside the corresponding route specs and allocate loopback ports dynamically.
• Normalize Vite module IDs so island bundling works with Windows paths.

What are the acceptance criteria?

• npm test
• npm run test:browser
• npm run lint
• npm run types
• npx wrangler deploy --dry-run

This adds test coverage and cross-platform build normalization; it does not change the rendered UI, so before/after screenshots are not applicable.

[MattIPv4]

Thanks for working on this! Instead of unstable_dev, I wonder if we can use the new createTestHarness designed for use w/ Playwright etc.? https://developers.cloudflare.com/changelog/post/2026-07-21-integration-test-harness/

[MattIPv4]

Instead of a dedicated spec file for the human outputs, I think it'd be good to include this as part of the existing spec files for each route, if possible? Or, if not, at least have a dedicated browser spec file alongside each existing route/spec?

[snowyukitty]

Addressed both suggestions: the browser suite now uses createTestHarness(), and the assertions live in route-adjacent api.browser.spec.ts and library.browser.spec.ts files. I also incorporated current master (through #261) and kept the browser setup aligned with the WEBSITE_BASE route contract.

Fresh current-base checks pass: Chromium 2/2 twice, unit tests 485/485, types, lint, focused formatting, a Wrangler dry run, and git diff --check. Thanks!