Add social share card (og:image) across all pages + summary_large_image

Brand-accurate 1200x630 OG card (ShopWisdom wordmark, navy serif headline with
amber 'doesn't have to', navy footer band). Wires og:image/twitter:image on the
homepage, Continuity Audit, and the above/below article so shared links render a
card instead of a blank preview. SVG source kept alongside. Staging branch only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

index.html

@@ -16,9 +16,14 @@
 <meta property="og:description" content="Your best people are retiring. We help Canadian manufacturers capture the know-how that lives in a few heads and turn it into systems the whole shop can use — before it walks out the door.">
 <meta property="og:url" content="https://shopwisdom.ca/">
 <meta property="og:locale" content="en_CA">
-<meta name="twitter:card" content="summary">
+<meta property="og:image" content="https://shopwisdom.ca/og-card.png">
+<meta property="og:image:width" content="1200">
+<meta property="og:image:height" content="630">
+<meta property="og:image:alt" content="Shop Wisdom — your best people are retiring. Their know-how doesn't have to.">
+<meta name="twitter:card" content="summary_large_image">
 <meta name="twitter:title" content="Shop Wisdom — keep what your best people know">
 <meta name="twitter:description" content="Knowledge continuity for Canadian manufacturers — before it walks out the door.">
+<meta name="twitter:image" content="https://shopwisdom.ca/og-card.png">
 <script type="application/ld+json">
 {
   "@context": "https://schema.org",