Adds support for terminal progress indicators using the OSC 9;4 escape sequence. This displays task completion progress in the terminal window chrome (tabs, title bars) for compatible terminals.

Key features:
- Real-time progress updates as tasks complete
- Automatic cleanup on TUI exit
- Uses ST terminator for maximum compatibility
- Writes to stderr to avoid conflicts with TUI rendering

Supported terminals:
- Ghostty (full support)
- Windows Terminal v1.6+ (full support)
- VTE-based terminals like GNOME Terminal and Ptyxis (full support)
- Other terminals gracefully ignore the sequences

cleanup(core): consolidate terminal progress clearing in app instance

Add std::io::Write to top-level imports in lifecycle.rs and app.rs, move restore_terminal to instance method on AppLifeCycle to reuse app.clear_terminal_progress() instead of duplicating logic, and remove redundant local imports from functions.

cleanup(core): remove redundant progress update in start_tasks

The terminal progress indicator only changes when tasks transition from incomplete to completed states. Starting tasks (NotStarted → InProgress) doesn't change the percentage, making this call redundant.

cleanup(core): cache incomplete task count for progress calculation

Maintain incomplete_task_count on the App struct instead of recalculating it every time we update terminal progress. This avoids iterating through the entire task_status_map on each status update.

cleanup(core): cache incomplete task count for progress calculation

Maintain incomplete_task_count on the App struct instead of recalculating it every time we update terminal progress. This avoids iterating through the entire task_status_map on each status update.

cleanup(core): cache incomplete task count for progress calculation

Maintain incomplete_task_count on the App struct instead of recalculating it every time we update terminal progress. This avoids iterating through the entire task_status_map on each status update.

cleanup(core): move restore_terminal back to standalone function

Make clear_terminal_progress a static method in App so it can be called without an instance. Convert restore_terminal back to a standalone #[napi] function in lifecycle.rs rather than an instance method on AppLifeCycle.