Add /api/predictions/:id/share metadata for social previews

[greatest0fallt1me]

Description

This is a backend issue for the GrantFox campaign. This is a backend issue for the GrantFox campaign. Return OG/Twitter card-ready metadata.

Requirements and Context

• Implement per the description
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/predictions-share-meta

2. Implement changes
   • src/routes/predictions/share.ts (new)
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

feat: predictions share metadata

Acceptance Criteria

• Implementation matches the description
• Tests added and passing
• Code review approved
• Docs updated

Guidelines

• Minimum 90% test coverage on changed lines
• Input validation at the boundary; standardized error envelope
• Structured logging with correlation IDs
• Clear documentation and inline comments
• Timeframe: 96 hours