fix(ui): update button styles and labels

[m-dilorenzi]

Description

Minor UI/style adjustments across several standalone components to improve visual consistency and clarity of labels and buttons.

Changes

Components

• NeStepper: added an optional labelColorClasses prop (default text-primary-600 dark:text-primary-500) so the step label color can be customized.
• NatRulesContent: the create-rule button changed from kind="secondary" to kind="primary"
• IpsSuppressedAlerts: the add button now uses the faBellSlash icon instead of faCirclePlus, and its label was switched from add_bypass to add_suppressed_alert (both in the toolbar and in the empty state).
• SshKeys: added a "public keys" label (ssh_keys.public_keys_label) shown above the list when at least one key
  exists.
• WireguardPeerTunnelList: the add-tunnel button changed from kind="secondary" to kind="tertiary".

i18n

• en.json / it.json: renamed the SSH key label from "Add new SSH key" → "New SSH key" ("Aggiungi nuova chiave SSH" → "Nuova chiave SSH").