fix(footer): sync catalog stats with templates.json (extensions count)

[ulises-jeremias]

Context

Homepage stats and the footer disagree: stats-bar.tsx shows the live catalog counts, while layout-shell.tsx hardcodes an outdated extensions count (8 vs 12).

Steps

1. Compare src/components/stats-bar.tsx and src/components/layout-shell.tsx.
2. Align footer numbers with the catalog (5 templates / 12 extensions / categories as in registry) — prefer sharing one source of truth instead of two hardcodes.
3. Confirm mobile footer still looks fine.

Acceptance criteria

• Footer stats match homepage stats bar
• Counts match cpa-templates/templates.json on main at time of PR
• Prefer deriving shared stats (helper or shared constant) over duplicate magic numbers
• No visual regression on desktop/mobile footer

Files

• src/components/layout-shell.tsx
• src/components/stats-bar.tsx
• Optional: src/lib/data.ts

How to verify

Load homepage and check header/stats + footer numbers match.