QoL: taskbar progress, animated title spinner, and configurable completion sound

[aboimpinto]

Quality of Life: Taskbar progress, title animation, and completion sound

Three small QoL features that give visual and audible feedback during/after processing, so the user can alt-tab away and still know when work is done.

Feature 1: Taskbar progress indicator

While the model is thinking or executing tools, Windows Terminal shows a green indeterminate progress bar on the taskbar icon via OSC 9 ; 4 ; 1. The bar is cleared on completion via OSC 9 ; 4 ; 0.

Feature 2: Animated terminal title

Cycles the terminal tab title between 🐳 and 🐋 every 800ms during processing (matching the whale status indicator in the TUI header). Shows ✅ DeepSeek TUI on completion (only in beep mode). Clears on next key press or mouse click.

Feature 3: Completion sound

Plays a short sound when every turn finishes, regardless of duration (unlike the existing [notifications] system which only fires for long turns exceeding a threshold).

Configurable via [notifications] completion_sound in config.toml:

Mode	Behavior	Visual indicator
beep (default)	System notification sound (MessageBeep on Windows, BEL on other platforms)	✅ title marker shown
bell	Raw terminal BEL character (\x07)	No ✅ title marker (bell is its own terminal-level indicator)
off	Silent	No ✅ title marker

Implementation

• crates/tui/src/tui/notifications.rs — set_taskbar_progress(), start_title_animation(), stop_title_animation(), play_completion_sound(), CompletionSound enum handling
• crates/tui/src/core/engine/turn_loop.rs — hook at turn start
• crates/tui/src/tui/ui.rs — hook at turn end + user interaction (clears ✅ marker)
• crates/tui/src/config.rs — CompletionSound enum + config field

[aboimpinto]

Implemented in #1872