Implement automatic calculation of plan metrics

Related to #43

Implement automatic calculation and display of practice plan metrics with dynamic updates and manual adjustments.

Add functions to calculate estimated time, player range, skill level range, and complexity level distribution in src/routes/practice-plans/create/+page.svelte.
Add a new section to display these metrics using appropriate UI components like progress bars and charts.
Add input fields or sliders next to each metric for manual adjustments.
Set up event listeners and reactive statements to recalculate metrics when drills are added, removed, reordered, or break durations are modified.
Implement error handling and validation logic to handle edge cases and provide user feedback for calculation errors or inconsistencies.

For more details, open the Copilot Workspace session.

austeane / qdrill