Apply the megamenu feedback round (develop) - #225

Related to T51ENG-2081

Proposed changes

• Align the header and megamenu content width across environments by moving the .wrapper 5vw inset from production's Customizer CSS into the theme (desktop only), and align panel content to the header content edge
• Desktop panels: two columns of links (was three), wider featured column with a vertical divider, thin line between header and panel, full-bleed white veil while a panel is open
• Featured card: image on top, heading below it, custom description text field (falls back to the excerpt), and a custom link field rendered as a green "Learn More" link
• Switch all megamenu accents to the brand green (brand-color-1), reserving the link green for hover states
• Mobile menu redesign per the provided specs
• Remove dead code

Why are these changes being made?

• Partner feedback round (see Linear issue)

Testing instructions

• Desktop (≥1200px): hover a megamenu item — panel content should align exactly with the logo/nav edges; two columns of links; featured card shows image, green heading, title, text, green "Learn More →"
• In Appearance → Menus, set "Featured text" and "Featured link" on a megamenu item to verify the custom overrides; clear them to verify the excerpt/"Learn More" fallbacks
• Hover menu links: color change only, no text shifting or underline (top-level keeps the green underline)
• Check Mobile (<1200px): open the hamburger — white full-screen menu, logo row stays visible, tapping a row expands it, opening another menu closes the first, sticky green "Get Involved" pill at the bottom links to /get-involved/