feat(collections): add real-time updates via WebSocket (Limitation #4)

Implement real-time collection updates when books are added/removed:

Backend Changes:
- Added connManager to CollectionHandler struct
- Updated constructor to accept ConnectionManager
- Updated all NewCollectionHandler() calls in ebook.go and main.go
- Added WebSocket broadcasts in AddBooks() handler
- Added WebSocket broadcasts in BulkRemoveBooks() handler
- Broadcasts collection_updated events with:
  - collection_id: Which collection changed
  - action: books_added or books_removed
  - book_ids: Array of affected book IDs
  - count: Number of books changed

Frontend Changes:
- Added WebSocket connection in collections UI
- connectWebSocket() establishes connection to /ws/sync
- Listens for collection_updated events
- Shows toast notification on collection change
- Auto-reloads page after 1 second to show updated book list
- Auto-reconnect on disconnect (5s delay)
- Error handling for WebSocket failures

WebSocket Event Format:
{
  "type": "collection_updated",
  "timestamp": "2026-02-01T12:00:00Z",
  "data": {
    "collection_id": "uuid",
    "action": "books_added",
    "book_ids": ["uuid1", "uuid2"],
    "count": 2
  }
}

User Experience:
- When another user adds books to a collection, all connected clients see:
  1. Toast notification: "Collection updated: books_added (2 books)"
  2. Page auto-refreshes after 1 second
  3. Updated book list displays
- Same for book removal
- Works across multiple browser tabs/devices
- No manual refresh needed

Technical Notes:
- Broadcasts to ALL connected WebSocket clients
- Client-side filtering by collection_id
- Existing progress/conflict broadcasts continue to work
- Connection manager handles broadcast distribution

Resolves Limitation #4: Real-time Collection Updates

templates/collections.templ

@@ -335,11 +335,46 @@ templ CollectionDetail(user User, collection CollectionDetailData, books []BookD
                     },
                 }{ end }
             ];
+            let ws = null;
 
             function backToCollections() {
                 window.location.href = '/collections';
             }
 
+            function connectWebSocket() {
+                const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
+                const wsUrl = `${protocol}//${window.location.host}/ws/sync`;
+
+                ws = new WebSocket(wsUrl);
+
+                ws.onopen = function() {
+                    console.log('WebSocket connected');
+                };
+
+                ws.onmessage = function(event) {
+                    const message = JSON.parse(event.data);
+
+                    if (message.type === 'collection_updated' && message.data.collection_id === collectionId) {
+                        showToast(`Collection updated: ${message.data.action} (${message.data.count} books)`, 'info');
+
+                        setTimeout(() => {
+                            location.reload();
+                        }, 1000);
+                    }
+                };
+
+                ws.onclose = function() {
+                    console.log('WebSocket disconnected, reconnecting in 5s...');
+                    setTimeout(connectWebSocket, 5000);
+                };
+
+                ws.onerror = function(error) {
+                    console.error('WebSocket error:', error);
+                };
+            }
+
+            connectWebSocket();
+
             function filterCollectionBooks() {
                 const searchTerm = document.getElementById('collection-search').value.toLowerCase();
                 const booksContainer = document.getElementById('books-container');