Build mood trend aggregation function

Create a TypeScript function that analyzes a user's mood journal entries over time and returns a structured trend report.

analyzeMoodTrends(entries: MoodEntry[]): TrendReport

// MoodEntry: { date: string (ISO), mood: 1 | 2 | 3 | 4 | 5, note?: string }
// TrendReport: {
//   average: number,
//   trend: 'improving' | 'declining' | 'stable',
//   streaks: { best: number, current: number },  // consecutive days with mood >= 4
//   volatility: number,  // standard deviation of mood scores
//   weeklyAverages: { week: string, avg: number }[]  // ISO week string
// }

Trend logic:

• Compute a 7-day moving average
• 'improving' if the last MA value is >= 0.3 higher than the first MA value
• 'declining' if >= 0.3 lower
• 'stable' otherwise
• Return trend: 'stable' and empty arrays if fewer than 3 entries

Write unit tests for 5 scenarios: improving trajectory, declining trajectory, stable, single entry, empty input.