Webapp: Command bar with scopes and quick actions

Command bar rebuilt with scoped search, quick actions, and keyboard navigation.

• Open with Cmd+K from anywhere, Spotlight-style frosted glass design
• Scope bar: filter by Messages or Actions, switch with Cmd+1 through Cmd+4
• Quick actions surface pages and settings with breadcrumb paths
• Recent searches saved automatically, clear individually or all at once
• Results update as you type with no delay
• State resets on every open
• Fixed missing translations on the error page