Emit section difficulty events for sectionmap integration

[carochacs]

Summary

Adds event emission of section difficulty data to enable the sectionmap plugin to display glass-filling difficulty visualization for each song section.

Changes

• Add calculateAndEmitSectionDifficulties() function to compute difficulty metrics per section
• Calculate section difficulty based on phrase data within each section's time range
• Determine appropriate glass size (small/medium/large) based on difficulty
• Emit difficulty:sections-updated event with section difficulty map
• Emit updated data whenever mastery changes or song loads
• Export function for testing

Data Structure

Each section receives difficulty data with:

• fillPercentage: 0-100 value representing how much the glass fills (based on mastery vs max difficulty)
• glassSize: from 1 to 5 - determined by section's relative difficulty
• avgDifficulty: Average difficulty of phrases in section
• maxDifficulty: Maximum difficulty of phrases in section

Event Contract

Plugins listen for the event via:

window.feedBack.on('difficulty:sections-updated', (event) => {
    const { sectionDifficulties, mastery, maxDifficulty } = event.detail;
    // Use sectionDifficulties map to render section-specific visualizations
});

This enables seamless integration with the sectionmap plugin for unified section difficulty visualization.

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