Dark mode background is washed-out grey with low contrast

--color-background-dark: #2b2b2b in src/styles/global.css produces a washed-out mid-grey background. Paired with the grey body text it gives low contrast and reads as "dark mode not finished" rather than a designed dark theme.

Suggested fix

• Move the background to near-black (~#0b0b0d).
• Introduce a separate slightly-lighter surface token for cards and elevated elements, so cards are distinguishable from the page.
• Re-check text and link contrast against WCAG AA after the change.

Screenshot: https://api.wallfacer.ai/captures/019fb00b-b916-71a5-8c70-8858013b72c5?signature=761ff6490e478ee5799dc7966a13470cbe90919a2bc3d3c672e2c6cfb58ce276