feat: migrate CoreLink to link.coreplatform.ir

[jaavid]

Summary

Moves the CoreLink website from the legacy corelinkplatform.ir hostname to the product-family hostname link.coreplatform.ir.

Changes

• GitHub Pages custom domain (public/CNAME) -> link.coreplatform.ir
• canonical/OpenGraph metadata -> link.coreplatform.ir
• robots/sitemap URLs -> link.coreplatform.ir
• SEO quality tests updated to enforce the new canonical host
• README and deployment contract updated
• corelinkplatform.ir documented as a legacy hostname that should permanently redirect to https://link.coreplatform.ir

Deployment intent

link.coreplatform.ir becomes the only GitHub Pages custom domain for this repository. The old apex domain should be handled as a Cloudflare edge redirect, not a second Pages custom domain.

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