Rework priority estimation GitHub action according to reach/impact/effort methodology

[Copilot]

This PR completely reworks the priority estimation logic in the GitHub action to use a new reach/impact/effort methodology as specified in the project roadmap estimation documentation.

Changes Made

🔄 Updated Priority Calculation Formula

Before: Simple priority labels + days old

const basePriority = Math.min(...labels.map(l => labelWeights[l] || 10), 1000);
const finalScore = basePriority + daysOld;

After: Reach/Impact/Effort methodology

Priority Score = (Reach × Impact) / Effort

📊 New Label Mappings

• Reach (user/stakeholder impact): reach:high (100), reach:medium (75), reach:low (50)
• Impact (value/benefit): impact:high (200), impact:medium (137.5), impact:low (75)
• Effort (work required): effort:high (10), effort:medium (5), effort:low (2)

🎯 Example Validation

The implementation correctly handles the example from the issue:

Labels: reach:low
Calculation: (50 × 137.5) / 5 = 1,375 ✅

🛡️ Robust Fallback Logic

• Gracefully handles missing labels with sensible defaults
• Preserves existing GraphQL project integration
• Enhanced logging for debugging and validation

Testing

Created comprehensive test documentation with 15 test cases covering:

1. Basic scenarios: All combinations of reach/impact/effort values
2. Missing labels: Fallback behavior validation
3. Edge cases: Boundary conditions, multiple labels, min/max scores
4. Complex scenarios: Label updates, conflicting labels, relative priorities

Example test cases:

• High priority: reach:high + impact:high + effort:low → 10,000
• Low priority: reach:low + impact:low + effort:high → 375
• Missing labels: Uses defaults to ensure calculation never fails

All test cases have been validated locally and include step-by-step instructions for manual verification.

Files Modified

• .github/workflows/priority-score.yml - Updated action with new calculation logic
• priority-estimation-tests.md - Comprehensive test cases and validation guide

The action maintains full backward compatibility with the existing project board integration while providing more nuanced and accurate priority scoring.

Fixes #2614.

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