feat(pass): allow copying multiple login fields at once

[PAX-1-2]

Description

Copying several fields of a login item currently requires copying them one by one. This adds a multi-copy mode to the login item detail view:

• A "Select fields to copy" toggle in a small toolbar above the item fields.
• While enabled, every copyable field (email, username, password, TOTP token, each website, note and custom fields) shows a checkbox in place of its icon, and per-field click-to-copy is temporarily disabled to avoid accidental copies.
• A separator checkbox controls the output format: Label: value entries joined either by ", " (comma and space) or by line breaks.
• Select all / deselect all, and a copy action that reuses the existing copyToClipboard flow (respects the clipboard TTL setting and notifications).

Example output: Email: user@example.com, Username: john or the same with one field per line.

Implementation notes

• New MultiCopy.tsx in packages/pass/components/Item/MultiCopy/ exporting the useMultiCopy hook, the selection checkbox and the toolbar.
• Login.content.tsx builds the list of selectable fields and swaps the field icon for the selection checkbox while the mode is enabled.
• ExtraFieldsControl gained two backwards-compatible optional props (copyable, renderIcon); OTPValueControl/UpgradeControl accept a ReactElement icon.
• TOTP tokens are resolved lazily at copy time via core.generateOTP, so no extra OTP subscriptions are introduced.
• Translations for the new strings can be provided through Crowdin.

Testing

• Built and manually tested the Firefox extension (temporary add-on load).
• prettier --check, eslint and tsgo (check-types) pass on the changed files.