Bump all customer-facing references to the managed base plan price from
$10/month to $20/month, and scale the bundled "Includes $X of Usage
Credits" copy from $10 to $20 to match the price.
Covers the subscribe/billing pages, onboarding plan card and fact sheet,
backlinks/AI-search access gates, and the marketing pricing/comparison/
GSC pages plus the README.
Claude-Session: https://claude.ai/code/session_017QayWXGubs1JNbLbqRF4CS
Co-authored-by: Claude <noreply@anthropic.com>
