feat(web): native share sheet for created + saved links

Adds a "Share link" button that invokes navigator.share() so iOS
home-screen PWA users (and any platform with the Web Share API)
get the system share sheet — AirDrop, Messages, Mail, WhatsApp…
Falls back to copy-only on platforms without support.

Wired on both CloudSharePanel (just-created link) and Settings →
Shared links (re-share an existing one).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/components/CloudSharePanel.tsx

@@ -71,6 +71,20 @@ export default function CloudSharePanel() {
     setTimeout(() => setCopied(false), 1500);
   };
 
+  const canShare = typeof navigator !== "undefined" && typeof navigator.share === "function";
+
+  const share = async (url: string, fileName: string) => {
+    try {
+      await navigator.share({
+        title: `AnyDrop — ${fileName}`,
+        text: "File shared via AnyDrop",
+        url,
+      });
+    } catch {
+      // User canceled the share sheet, or the browser rejected — nothing to do.
+    }
+  };
+
   return (
     <div className="paper-panel p-4 sm:p-5">
       {stage.kind === "idle" && (
@@ -235,13 +249,27 @@ export default function CloudSharePanel() {
             </div>
           </div>
 
-          <button
-            onClick={() => copy(stage.shareUrl)}
-            className="w-full py-2.5 bg-ink text-paper text-sm font-medium rounded-sm
-                       hover:bg-signal transition-colors duration-fast ease-crisp"
-          >
-            {copied ? "Copied ✓" : "Copy link"}
-          </button>
+          <div className="flex gap-2">
+            {canShare && (
+              <button
+                onClick={() => share(stage.shareUrl, stage.fileName)}
+                className="flex-1 py-2.5 bg-ink text-paper text-sm font-medium rounded-sm
+                           hover:bg-signal transition-colors duration-fast ease-crisp"
+              >
+                Share link →
+              </button>
+            )}
+            <button
+              onClick={() => copy(stage.shareUrl)}
+              className={`py-2.5 text-sm font-medium rounded-sm transition-colors duration-fast ease-crisp ${
+                canShare
+                  ? "flex-1 border border-paper-edge hover:border-ink text-ink"
+                  : "w-full bg-ink text-paper hover:bg-signal"
+              }`}
+            >
+              {copied ? "Copied ✓" : "Copy link"}
+            </button>
+          </div>
 
           <p className="mt-2 font-mono text-[11px] text-ink-faint break-all">
             {stage.shareUrl}

web/src/pages/Settings.tsx

@@ -509,6 +509,22 @@ function SharedLinksSection() {
     setTimeout(() => setCopiedId((v) => (v === item.id ? null : v)), 1500);
   };
 
+  const canShare = typeof navigator !== "undefined" && typeof navigator.share === "function";
+
+  const onShare = async (item: LinkItem) => {
+    if (!item.keyFrag) return;
+    const url = `${window.location.origin}/r/${item.id}#k=${item.keyFrag}`;
+    try {
+      await navigator.share({
+        title: `AnyDrop — ${item.filename ?? "Encrypted file"}`,
+        text: "File shared via AnyDrop",
+        url,
+      });
+    } catch {
+      // User canceled — no-op.
+    }
+  };
+
   return (
     <section className="mb-12">
       <div className="text-xs uppercase tracking-[0.22em] text-ink-muted">
@@ -554,6 +570,14 @@ function SharedLinksSection() {
                   </div>
                 </div>
                 <div className="flex flex-col items-end gap-1.5 shrink-0">
+                  {item.keyFrag && status === "active" && canShare && (
+                    <button
+                      onClick={() => onShare(item)}
+                      className="text-xs text-ink hover:text-signal transition-colors"
+                    >
+                      Share →
+                    </button>
+                  )}
                   {item.keyFrag && status === "active" && (
                     <button
                       onClick={() => onCopy(item)}