feat: support custom og:image for social sharing

[Clapboiz]

Type of change

• Bug fix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other (please describe):

Checklist

• I have read the CONTRIBUTING document.
• I have checked to ensure that this Pull Request is not for personal changes.
• I have performed a self-review of my own code.
• My changes generate no new warnings.

Related Issue

N/A (or link to your issue if you created one, e.g., #123)

Changes

• Added support for custom og:image in page/post frontmatter
• Updated layout/SEO component to use custom og:image
• Added fallback to a default image if no custom image is provided

How To Test

1. Run pnpm dev to start the local server
2. Open a post or profile page and inspect page source
3. Check that <meta property="og:image" content="..."> is set correctly
4. Test sharing the URL on Facebook Sharing Debugger or Twitter Card Validator

Screenshots (if applicable)

This is how the blog post preview looks before the change:

Before (current social preview)

After (with custom og:image)

My social blog background (used as og:image)

My blog background (not used for social preview anymore)

Additional Notes

• This change only affects social sharing previews
• No visual changes on the website

[vercel]

@Clapboiz is attempting to deploy a commit to the zephyirdgmailcom's projects Team on Vercel.

A member of the Team first needs to authorize it.