⚡ Bolt: Optimize StatsService aggregation queries

[google-labs-jules]

Optimizes StatsService to perform SUM aggregations for reading minutes and pages directly in the database, avoiding loading large datasets into memory. Uses existing GetTotalMinutesAsync repository method and direct DbContext access for pages sum, following established patterns.

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PR created automatically by Jules for task 14777551252098779145 started by @Tr1sma

[google-labs-jules]

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[Copilot]

Pull request overview

This PR optimizes the StatsService by performing database-side aggregation for reading statistics instead of loading entire datasets into memory. This addresses performance concerns when dealing with large numbers of books and reading sessions.

Key Changes:

• GetTotalMinutesReadAsync now uses the existing repository method GetTotalMinutesAsync instead of loading all sessions
• GetTotalPagesReadAsync uses direct DbContext access with SumAsync instead of loading all completed books
• New performance tests added to verify correctness of the optimized implementations

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
BookLoggerApp.Infrastructure/Services/StatsService.cs	Optimized two methods to use database-side SUM aggregation with helpful inline comments
BookLoggerApp.Tests/Services/StatsServicePerformanceTests.cs	Added new test file with tests verifying correctness of both optimized aggregation methods

Comments suppressed due to low confidence (1)

BookLoggerApp.Infrastructure/Services/StatsService.cs:240

• Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.

        if (category.HasValue)
        {
            // Sort by specific category
            sortedBooks = category.Value switch
            {
                RatingCategory.Characters => books.Where(b => b.CharactersRating.HasValue).OrderByDescending(b => b.CharactersRating),
                RatingCategory.Plot => books.Where(b => b.PlotRating.HasValue).OrderByDescending(b => b.PlotRating),
                RatingCategory.WritingStyle => books.Where(b => b.WritingStyleRating.HasValue).OrderByDescending(b => b.WritingStyleRating),
                RatingCategory.SpiceLevel => books.Where(b => b.SpiceLevelRating.HasValue).OrderByDescending(b => b.SpiceLevelRating),
                RatingCategory.Pacing => books.Where(b => b.PacingRating.HasValue).OrderByDescending(b => b.PacingRating),
                RatingCategory.WorldBuilding => books.Where(b => b.WorldBuildingRating.HasValue).OrderByDescending(b => b.WorldBuildingRating),
                _ => Enumerable.Empty<Book>()
            };
        }
        else
        {
            // Sort by average rating
            sortedBooks = books
                .Where(b => b.AverageRating.HasValue)
                .OrderByDescending(b => b.AverageRating ?? 0);
        }

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