Add watch mode (-w, --watch) for continuous monitoring #61

Feature Request

I would like to propose adding a watch mode feature that continuously monitors and displays Claude Code usage in real-time.

Proposed Solution

Add -w, --watch flag to all report commands (daily, monthly, session) that would:

• Continuously monitor the JSONL files for changes
• Automatically refresh the display when new usage data is detected
• Update the terminal output in-place (similar to tools like htop or watch command)

Example Usage

# Continuously monitor daily usage
ccusage daily --watch

# Short form
ccusage daily -w

# With other options
ccusage daily -w --breakdown --since 20250101

Implementation Details

• Refresh interval could be configurable (e.g., --watch 5 for 5 seconds)
• Should clear and redraw the table to avoid cluttering the terminal
• Pressing Ctrl+C would exit watch mode

Use Case

This would be particularly useful for:

• Real-time monitoring during active Claude Code sessions
• Dashboard-like displays on secondary monitors
• Tracking usage patterns throughout the day