Add explicit return-type annotation to the `BlogPost` page component

[ooloth]

Why

BlogPost in app/[slug]/page.tsx is exported without a return-type annotation at the Next.js route boundary, leaving its contract incomplete where other page components in the same project already annotate their return types.

Current state

app/[slug]/page.tsx line 37 exports async function BlogPost({ params }: Props) with no return type. The Likes and Blog page components in the same project already annotate their return types as Promise<ReactElement> or equivalent.

Ideal state

• BlogPost carries an explicit return type: Promise<ReactElement> (or the correct JSX type for this component).
• The signature is consistent with other page components in the codebase.
• A reader can understand the contract from the signature alone.

Starting points

• app/[slug]/page.tsx — line 37 (the function signature to annotate)
• Other page components (e.g., Likes, Blog) — reference for the return type used in the project

QA plan

1. Open app/[slug]/page.tsx and verify the BlogPost function signature includes a return-type annotation.
2. Change the return type to an incompatible type — expect a compile error.
3. Run tsc --noEmit — expect no type errors.

Done when

BlogPost has an explicit return-type annotation consistent with other page components in the project.