Better error messages for post character limit

[RafDevX]

Most fields (e.g., title, location, etc.) have type VARCHAR(255) in the database, which means they are already limited to 255 characters. However, it could be made more clear to the user that they are violating this, since they otherwise only receive an error "SQL transaction failed" without any further details.

The most basic possibility is to just add a maximum length requirement to the HTML form on the client-side, which should prevent them from writing too much.

However, in addition, it might also be nice to add validation on the server side and show an error message similar to when the minimum character count isn't respected.