Add animated braille spinner to terminal title when agent is running

[iamdavidhill]

Summary

• Adds a visual indicator in the terminal window title showing when the agent is actively processing
• Replaces the static "OC" prefix with an animated two-character braille spinner (⠋⠙ → ⠙⠹ → ⠹⠸ → ...) that cycles every 80ms while the session status is "busy"
• Returns to the static "OC" prefix when the agent finishes, with no visual jump since the spinner matches the width of "OC"

Details When viewing a session with a custom title, the terminal window title shows OC | Session Title. This change animates the "OC" portion with a fluid braille dot pattern while the agent is running, providing visual feedback that work is in progress without needing to look at the main TUI. The animation uses 10 frames of two-character braille patterns that create a smooth rotating effect. Proper cleanup is handled when navigating away, when the status changes to idle, or when the component unmounts.