feat(seo): add canonical, schema, social metadata and crawl fixes

[0xgthuva]

Add comprehensive onsite SEO improvements across the site.

Add self-referencing canonical URLs

Add Open Graph metadata for social sharing

Add Twitter large image card metadata

Add WebSite, WebPage, Organization, BreadcrumbList and BlogPosting JSON-LD

Add robots directives and improve robots.txt

Improve sitemap handling and exclude invalid or redirected URLs

Improve homepage title and meta description

Remove obsolete meta keywords

Normalize Open Graph tags to use the correct property attribute

Reuse existing generated social images for OG and Twitter cards

Add noindex handling for 404 and non-indexable pages

Redirect /audio-tools to /audio#audio-tools

Replace internal links pointing to legacy or redirected routes

Add an SEO validation script and pnpm seo command

Add SEO_PLAN.md with implementation and maintenance guidance

[vesaber]

dude u already got rejected once for the same thing
stop pr'ing ai slop

[nbats]

already explained to you in last one

[0xgthuva]

yes, I missed the last one
after I found out this curated website is very useful for me, I just wanted to contribute with my expertise, this PR was from my agent, but I did the changes, implemented the startegy, identified SEO opportunities, compiled all of them in one go and passed it to my agent.

maybe you can skip these - these are big codebase level changes, but others are just minor tweaks

• Redirect /audio-tools to /audio#audio-tools
• Replace internal links pointing to legacy or redirected routes
• Add an SEO validation script and pnpm seo command