Every page inherits canonical "/" from the root layout #115

Problem

app/layout.tsx sets

alternates: { canonical: "/" },

in the root metadata. Next.js merges metadata downward, so every page that doesn't set its own canonical (most of them) tells search engines "I am a duplicate of the home page". That can keep pages like /gsoc and /blog/<post> out of search results.

Done when

• The root layout no longer sets alternates.canonical. Keep it on the home page only: move it to app/page.tsx's metadata, or drop it.
• Spot-check with view-source on /, /gsoc and one blog post: none of them may claim <link rel="canonical" href="https://www.devforge.club/"> except /.
• npm run build passes.

Size: ~3–6 lines. Small diff, real impact: explain in the PR why it matters.

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