[Translation Phase 2] Action sheet UX improvements – bold title, smart placement, single-language auto-translate

[data-sync-user]

Addresses UX feedback on the translation language picker action sheet:                         

• Bold title: "Translate Page to…" is now rendered in bold using DefaultDynamicFontHelper so it scales correctly with Dynamic Type accessibility settings.                                    
• Popover placement: When anchored to the toolbar button on iPad, the popover now uses [.up, .down] arrow directions so iOS automatically positions it above or below the button depending on available space, preventing it from covering the button.
• iOS 26 safety: The view fallback popover source (used when triggered from the main menu) is skipped on iOS 26+, where UIKit handles presentation without requiring an explicit source.     
• Singlelanguage autotranslate: When tapping the toolbar translate button and the user has exactly one preferred language configured, the action sheet is skipped and the page translates directly. This aligns the toolbar button path with the existing main menu behavior.
• Consistency fix: Both the toolbar button path (middleware) and the main menu path coordinator) now use TranslationConfiguration.isMultiLanguageFlow as the single source of truth for deciding whether to show the picker.

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