Input injection for signup table

[NilsJacobsen]

Fix what marc suggested

[NiklasBuchfink]

Error message, with invalid string

[NiklasBuchfink]

According to ChatGPT:
"Airtable prevents SQL injections by treating the filter formulas of the select() method as a special JSON query syntax instead of converting them directly to SQL. This JSON syntax is then converted into a secure query to the Airtable API.

SQL special characters such as quotes, semicolons, or comments cannot be used in Airtable filter formulas, which prevents SQL injections. Instead, Airtable provides a set of functions and operators that can be used in the filter formula to perform complex queries."

Added syntax check for email format to airtable request.
Also the input field itself also rejects malicious emails.

For this reason, I will close this issue.