Language handling and notification fixes, stronger cleanup of deleted voice data

This pass focuses on issues affecting people who work across multiple languages.

• Fixed AI conversations in English getting Korean titles — quoting another language in a chat no longer changes the title's language
• Fixed speech recognition being forced to a specific language on devices set to an unsupported language — it now auto-detects what you actually speak
• Improved how the first-visit language is chosen from your browser settings — a language you pick yourself always wins
• Fixed all-day event reminders not arriving in some time zones (London, Berlin, and others)
• Server-side cleanup of voice transcripts now also covers recordings attached to notes you deleted
• Documents in unsupported formats are no longer rendered as links
• Corrected the governing-law wording in the Japanese privacy policy
• Plus English copy refinements and general stability improvements