[Analytics Hub] Update colors for delta tag and chart with 0% change

[rachelmcr]

Closes: #8243

Description

This updates the Analytics Hub to use a gray color (instead of red) for stats with a 0% change from the previous period:

• 0% delta tag has a light gray background with black text.
• 0% chart has a dark gray line.

Changes

• The colors are now computed properties on DeltaPercentage.Direction, since they are inherently linked to the delta direction.
• Each of the three colors (delta background color, delta text color, and chart color) are set on the relevant cards in the Analytics Hub.

Note: The original idea behind DeltaPercentage was to just be a representation of the formatted string/direction in StatsDataTextFormatter. Given that so many report card values depend on the DeltaPercentage, I think it makes sense to extract that struct from the formatter as its own entity. Then, we can pass the DeltaPercentage itself to the analytics card view models (rather than passing each of the values separately). I'll open a separate PR so we can review that idea.

Testing

1. Ensure you have at least one stat in the Analytic Hub with 0% change from the previous period.
2. Build and run the app.
3. Tap "See more" on the My Store dashboard.
4. Confirm the 0% stat uses gray colors for the delta tag and chart.

Screenshots

Before	After

Submitter Checklist

Update release notes:

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

You can test the changes from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr8317-f7334be on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[ealeksandrov]