Implement YEC 2025 Takeover for Desktop Stable

Creating this ticket to have a parent ticket

Launch date for YEC 2025 is October 14.

Each year from ~mid-October through the end of December, the Tor Project runs its year-end fundraising campaign (aka "YEC"). This is the time during which we raise the most money per year from individual donors. A key strategy in this campaign is a branded takeover of about:tor (desktop + mobile) that includes the year-end campaign "mini brand," new assets, a fundraising message, and a donate button.

• Figma files for inspection:
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  • Last year's ticket for reference: YEC 2024 Takeover for Desktop Stable

cc/ @nicob @gaba @bella @morgan