Fix calculateWeeklyTrend bug by averaging sums (#1215)

[bhavyapandiya29]

Description

This PR resolves the math/logic error in the calculateWeeklyTrend function within src/lib/coding-activity-insights.ts. Previously, the function compared the raw sums of a 4-day period against a 3-day period, incorrectly resulting in an "up" trend for perfectly stable activity. The sums are now correctly divided by the number of days to yield a daily average before performing the trend comparison.

Fixes #1215.

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[bhavyapandiya29]

Hi @Priyanshu-byte-coder I have made a PR for this issue. Kindly review and merge it.

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