Add "Share Current Room" button to copy existing room config as share code

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

src/lib/components/Settings.svelte

@@ -358,6 +358,17 @@
     roomCreateMessage = "Room joined! Fields have been auto-filled.";
   }
 
+  async function handleShareCurrentRoom() {
+    const code = encodeShareCode(syncUrl, syncRoom, syncPassphrase);
+    shareCode = code;
+    try {
+      await navigator.clipboard.writeText(code);
+      roomCreateMessage = "Share code copied to clipboard!";
+    } catch {
+      roomCreateMessage = "Share code generated. Copy it from the field below.";
+    }
+  }
+
   async function copyShareCode() {
     try {
       await navigator.clipboard.writeText(shareCode);
@@ -826,13 +837,22 @@
         </div>
         {#if syncEnabled}
           <div class="room-actions">
-            <button
-              onclick={handleCreateRoom}
-              disabled={roomCreating}
-              class="secondary"
-            >
-              {roomCreating ? "Creating..." : "Create Room"}
-            </button>
+            <div class="room-buttons-row">
+              <button
+                onclick={handleCreateRoom}
+                disabled={roomCreating}
+                class="secondary"
+              >
+                {roomCreating ? "Creating..." : "Create Room"}
+              </button>
+              <button
+                onclick={handleShareCurrentRoom}
+                disabled={!syncUrl.trim() || !syncRoom.trim() || !syncPassphrase.trim()}
+                class="secondary"
+              >
+                Share Current Room
+              </button>
+            </div>
             <div class="join-row">
               <input
                 type="text"
@@ -1086,6 +1106,11 @@
     margin-bottom: 12px;
   }
 
+  .room-buttons-row {
+    display: flex;
+    gap: 8px;
+  }
+
   .join-row {
     display: flex;
     gap: 8px;