fix(security): Escape email addresses in mailto() to prevent XSS

Email columns in bootstrap tables had escaping disabled (line 52) and
mailto() function doesn't escape its parameters. This fix escapes email
addresses before passing to mailto() in:
- get_person_data_row() (employees)
- get_customer_data_row() (customers)
- get_supplier_data_row() (suppliers)

Attack vector: Malicious email via CSV import renders XSS in table view.
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f