Add autocomplete control and multiple-email support to settings fields

[steffenbew]

Motivation

• Prevent unwanted browser autofill on sensitive settings and improve input semantics for email notification fields.
• Allow entering multiple notification email addresses with proper email input type and validation.

Description

• Added autocomplete="off" to the main settings form in components/settings-page/index.php to disable form autofill.
• Enabled an autocomplete attribute (defaulting to off) for password fields in includes/core/settings/field-password/index.php.
• Made the text field template configurable via input_type, added autocomplete support, and added optional multiple handling in includes/core/settings/field-text/index.php.
• Updated settings registration in includes/features/class-settings-page.php to set input_type => 'email', multiple => true, and autocomplete => 'email' for notification email fields, and set autocomplete => 'off' for other sensitive fields.

Testing

• No automated tests were added or executed for this change.

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Codex Task