[FEATURE]: Implement Server-Side Analytics & Trend Reports

[rach-kanc]

📝 Pull Request Summary

This PR migrates the heavy data calculations for the Analytics Dashboard from the client's browser to the backend, fulfilling the "Enhanced Analytics" milestone on the project roadmap.

Key changes include:

• Added firebase-admin to securely execute database queries on the server without strict client rules.
• Created a high-performance Next.js API route (app/api/analytics/route.ts) that verifies the user's Auth token and calculates their total entries, streaks, and most common moods entirely on the server.
• Developed a custom useServerAnalytics hook to fetch this data.
• Updated BentoDashboard and MoodStats to prioritize server-rendered analytics while maintaining local Zustand state as an instant fallback for an optimal offline experience.

🔗 Related Issue

Closes #276

🛠️ Type of Change

• 🚀 New Feature
• 🐛 Bug Fix
• 📄 Documentation Update
• 🎨 UI/UX Enhancement

✅ Contributor Checklist

• I have tested my changes locally.
• My code follows the Apple-level design guidelines.
• I have updated the README if necessary.
• (Apertre 3.0) I have added relevant badges/labels.

##Tags
database, ssoc26, hard

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[rach-kanc]

@Nitya-003 Check the PR and add respective tags