integrate IndexNow API for proactive search engine crawling

[GSiesto]

Description

This PR implements the IndexNow protocol to proactively notify search engines (such as Bing and Yandex) whenever pdflince.com is updated.

Context: Because Bing relies heavily on IndexNow to manage its crawl budget and discover updates efficiently, integrating this API ensures that new features and localized pages will be indexed almost instantly rather than waiting for organic bot discovery.

Changes:

• Generated an IndexNow verification key and added it as a static file [public/7a258aaa2a9b472bb6e97935fe5e82ca.txt] for ownership validation.
• Updated [src/app/robots.ts] to include the Host: instruction pointing to the IndexNow protocol endpoint, alerting search engine crawlers of its availability.
• Modified the GitHub Actions deployment workflow [.github/workflows/deploy.yml] to automatically dispatch an HTTP ping to the api.indexnow.org endpoint immediately upon a successful production build and CloudFront cache invalidation.

Fixes # (issue)

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Ran a local Next.js production build (npm run build) and verified the output of [out/robots.txt] correctly contains the Host: directive and verification key logic.
• Tested the curl command locally to ensure the api.indexnow.org endpoint successfully accepts the ping format (returns 200 OK) without errors.
• Verified that the verification key [.txt] file sits in the correct static root directory for domain ownership validation.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes