chore: use https repository metadata

[snkk2x-collab]

Summary

• Update the package repository metadata from the SSH GitHub form to a public HTTPS URL.
• Leave runtime code, dependencies, package version, entrypoints, type declarations, and lockfile unchanged.

Rationale

This repository is public, so npm consumers should be able to follow the source repository link without SSH or GitHub key setup.

Validation

• node -e "const p=require('./package.json'); if (p.repository !== 'git+https://github.com/josestg/rehype-code-title.git') throw new Error(JSON.stringify(p.repository)); console.log(p.repository)"
• git diff --check
• git ls-remote https://github.com/josestg/rehype-code-title.git HEAD
• pnpm install --ignore-scripts --lockfile=false
• pnpm test
• pnpm pack --dry-run