Improve logging

[kettanaito]

Would be nice to have a proper logging to let the developer know:

• When a new OG image is generated (and its output path).
• When OG generation is skipped due to cache.
• When OG imaged is re-generated due to related HMR update.

There's built-in logger in Vite, but I struggle to make it print anything. I suspect it only works when the build is run in a specific mode (e.g. debug mode). That won't do.