Fix story share thumbnail — generate moleskine-style OG image

[realproject7]

Summary

When a user shares a story link on Farcaster (or any platform), the thumbnail/preview image is broken. It should dynamically generate an OG image matching the home page's moleskine notebook design aesthetic.

Current behavior

The share preview shows a mostly blank beige card with partial text, no proper layout or branding.

Expected behavior

Generate a styled OG image per story that matches PlotLink's moleskine design:

• Beige/cream notebook background
• Story title in Lora serif font
• Author name, plot count, price info
• PlotLink branding

Implementation

• Add a dynamic OG image route (e.g. src/app/story/[id]/opengraph-image.tsx) using Next.js ImageResponse
• Style it to match the moleskine card aesthetic from the home page
• Reference dropcast for OG image generation patterns

Acceptance Criteria

• Sharing a story link on Farcaster/X shows a properly styled preview image
• Image matches PlotLink's moleskine design language
• Includes story title, author, plot count, price