feat: placeholder images, Nostr inbox, order lookup, SEO, bigger logo

- 5 SVG placeholder product images (minimal dark style with watermark initials)
- Seed data updated to reference .svg placeholders
- Nostr DM inbox in admin (Messages tab) with shop npub display
- GET /api/admin/nostr-info endpoint for shop pubkey
- My Orders page: customers look up orders by NIP-07 Nostr identity
- GET /api/orders/by-pubkey/:pubkey endpoint with hex validation
- SeoMeta component for OG/Twitter meta tags
- SEO meta on HomeView and ProductView
- Base OG meta tags in index.html
- "My Orders" link in shop header nav
- Splash logo doubled in size on desktop (680px max)

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

public/images/shadow-hoodie.svg

@@ -0,0 +1,10 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 600 800" width="600" height="800">
+  <rect width="600" height="800" fill="#141414"/>
+  <text x="300" y="420" text-anchor="middle" dominant-baseline="central"
+        font-family="Georgia, 'Times New Roman', serif" font-weight="100"
+        font-size="400" fill="rgba(255,255,255,0.08)" letter-spacing="-10">S</text>
+  <line x1="270" y1="480" x2="330" y2="480" stroke="#F7931A" stroke-width="1"/>
+  <text x="300" y="510" text-anchor="middle"
+        font-family="'Helvetica Neue', Helvetica, Arial, sans-serif" font-weight="300"
+        font-size="24" fill="rgba(255,255,255,0.5)" letter-spacing="4">SHADOW HOODIE</text>
+</svg>