spread stat cards across article: one per section

- Bar chart: after intro (early viewport)
- 5h card: after "They Knew"
- 2-3x card: after bullet list in "The Numbers"
- 3h+ card: after "Courts Are Catching Up"

New single-card shortcode addiction-stat with num/color/label params.
Removed grouped addiction-impact and addiction-stats shortcodes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

layouts/shortcodes/addiction-stat.html

@@ -0,0 +1,5 @@
+{{/* Single stat card — usage: {{< addiction-stat num="5h" color="#667eea" label="..." >}} */}}
+<div style="background:#f8fafc;border:1px solid #e2e8f0;border-radius:12px;padding:1.25rem 1.5rem;margin:2rem 0;display:flex;align-items:center;gap:1.25rem">
+  <div style="font-size:2.5rem;font-weight:800;line-height:1;color:{{ .Get "color" }};font-family:system-ui,sans-serif;min-width:4rem;text-align:center">{{ .Get "num" }}</div>
+  <div style="font-size:0.95rem;color:#475569;line-height:1.4;font-family:system-ui,sans-serif">{{ .Get "label" }}</div>
+</div>