[Scorecards] Add Scorecard timeline graphic to 2025 Methodology page

[zarino]

Add the graphic from the homepage, to:

• the “Summary” section (perhaps between “…draft methodology below.” and “Whilst every effort…”?)
• the top of the “Scoring process” section

On the 2025 Methodology page.

[lucascumsille]

Close with https://github.com/mysociety/caps/pull/680