feat(listing): make an offer (prefilled DM) + share listing

On the listing detail page, buyers get 'Make an offer' (opens the DM with the
seller pre-filled with an offer message about the listing) and 'Share listing'
(copies the URL). Replaces the redundant 'Message' button (Contact Seller is
already in the shared trade actions).

Gate: 101 tests, 0 errors/warnings, boot smoke green.

src/pages/ListingDetailPage.tsx

@@ -25,7 +25,6 @@ import { genUserName } from '@/lib/genUserName';
 import { cn } from '@/lib/utils';
 import {
   ArrowLeft,
-  MessageCircle,
   CheckCircle,
   RotateCcw,
   Trash2,
@@ -33,6 +32,8 @@ import {
   MapPin,
   Calendar,
   Tag,
+  Handshake,
+  Share2,
 } from 'lucide-react';
 
 /**
@@ -104,6 +105,17 @@ export default function ListingDetailPage() {
 
   const lightboxImages: LightboxImage[] = item.images.map((url) => ({ url, isOwner: isOwnListing }));
 
+  const offerMessage = `Hi! I saw your listing “${item.title}” on SkateSpots and I'd like to make an offer.`;
+
+  const handleShare = async () => {
+    try {
+      await navigator.clipboard.writeText(window.location.href);
+      toast({ title: 'Link copied', description: 'Share it with a skater.' });
+    } catch {
+      toast({ title: 'Could not copy the link', variant: 'destructive' });
+    }
+  };
+
   const handleRelist = async () => {
     try {
       await relist(item.event);
@@ -304,15 +316,23 @@ export default function ListingDetailPage() {
               <Card className="bg-black/90 border-white/10">
                 <CardContent className="p-4">
                   <ListingTradeActions item={item} />
+                  <Button
+                    variant="outline"
+                    size="sm"
+                    onClick={() =>
+                      navigate(`/messages/${npub}?message=${encodeURIComponent(offerMessage)}`)
+                    }
+                    className="mt-2 w-full gap-2 border-orange-500/40 text-orange-400 hover:bg-orange-500/10"
+                  >
+                    <Handshake className="h-4 w-4" /> Make an offer
+                  </Button>
                   <Button
                     variant="ghost"
                     size="sm"
-                    asChild
-                    className="mt-2 w-full gap-2 text-gray-400 hover:text-white"
+                    onClick={handleShare}
+                    className="mt-1 w-full gap-2 text-gray-400 hover:text-white"
                   >
-                    <Link to={`/messages/${npub}`}>
-                      <MessageCircle className="h-4 w-4" /> Message {displayName}
-                    </Link>
+                    <Share2 className="h-4 w-4" /> Share listing
                   </Button>
                 </CardContent>
               </Card>