Moved CTA between new features and schedule

[rrrr08]

Changes

• Moved "How you can help" section from bottom (nested under Process) to between "What features" and "Schedule"
• Changed heading from <h3> to <h2> to match the new top-level section structure
• No content or functionality changes — purely a reorganization for better UX

New page structure

1. What features will be in Django X.X?
2. How you can help ← moved here (more visible)
3. Schedule
4. Process

This change makes the call-to-action more prominent, potentially increasing contributor engagement by reducing the discovery path.

Fixes #2267

[sarahboyce]

Thank you for working on this issue. We will progress this issue with the following PR: #2275
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