LIN-2731 Add beta Web Attribution guide

[RathodDarshil]

Summary

• Adds a new /sdk/web guide based on the published @linkrunner/web 0.1.15 package.
• Marks Web Attribution as beta and directs access requests to support@linkrunner.io.
• Recommends the Linkrunner CDN so SDK fixes can ship without a customer code change or redeploy.
• Explains that the Next.js npm helper also loads the CDN browser bundle by default.
• Includes first-party proxy and data-domain setup, user identification, custom events, verification, storage behavior, and troubleshooting.
• Adds the Web SDK to navigation and links it from the docs home page.
• Links the npm package, Web SDK repository, and Shopify guide.

Sources

• Published package: https://www.npmjs.com/package/@linkrunner/web
• Tashvik docs PR: docs: document the web SDK first-party collection domain #195
• Shipped data-domain implementation: feat(sdk): route collection through a customer-named subdomain (data-domain) web-sdk#10
• Linear: https://linear.app/linkrunner/issue/LIN-2731/document-beta-web-attribution-sdk

Tashvik PR #195 extended the old Web SDK page, which used stale package and CDN names. This PR rebuilds the page from the current published package and carries over the valid first-party collection guidance.

Verification

• npm view @linkrunner/web confirms version 0.1.15, package exports, README, and CDN examples.
• npm run check:routes passes with 101 registered pages.
• mintlify broken-links reports the same 28 baseline findings on origin/main. The new page adds no failures.
• git diff --check passes.
• The CDN script returns 200.
• The collector preflight returns 204.
• The Web SDK GitHub repository returns 200.

Tooling note

The installed Mintlify CLI does not expose the repository build command. Its local dev command prepares the site, then exits with the existing TypeError: (intermediate value) is not iterable. Route and MDX link parsing still complete successfully.