Share button on the videos list

Sharing from here is the common case — you are looking at the thing you want to
send. Uses the native share sheet where there is one, otherwise copies, and the
link carries a filename so it ends in .mp4 for clients that read the URL rather
than the headers.

videos.html

@@ -66,12 +66,25 @@ function card(p) {
   if (p.video_url) {
     // A finished video was a dead end here: watch or download, and no way back
     // into the shots, the cutaways or the cut without knowing the URL.
-    cta += '<a class="btn" style="display:inline-block;text-decoration:none;margin-top:10px;margin-left:8px" href="/script.html?id='
+    cta += '<button type="button" class="btn" style="margin-top:10px;margin-left:8px" '
+        + 'data-share="' + encodeURIComponent(p.id) + '">Share</button>';
+    cta += '<a class="btn ghost" style="display:inline-block;text-decoration:none;margin-top:10px;margin-left:8px" href="/script.html?id='
         + encodeURIComponent(p.id) + '">Edit</a>';
     cta += '<a class="btn ghost" style="display:inline-block;text-decoration:none;margin-top:10px;margin-left:8px" href="'
         + esc(p.video_url) + '" download>Download</a>';
   }
 
+  // The file URL ends in /public with no filename. Headers are already right
+  // (video/mp4), but clients that sniff the URL string are not, and a filename
+  // query is accepted and ignored by the file service.
+  window.__shareUrl = window.__shareUrl || function (p) {
+    var u = p.cut_url || p.video_url || "";
+    if (!u) return "";
+    var slug = ((p.pet_name || "video") + " " + (p.title || "")).toLowerCase()
+      .replace(/[^a-z0-9]+/g, "-").replace(/^-|-$/g, "").slice(0, 40) || "video";
+    return u + (u.indexOf("?") < 0 ? "?" : "&") + "v=" + slug + ".mp4";
+  };
+
   return '<div class="item">'
     + '<div>' + media + '</div>'
     + '<div>'