feat(web): add real-time activity feed via SignalR

- Add ActivityHub and wire up SignalR in Program.cs
- Broadcast new context events from ContextController
- Connect SignalR client on Analytics page for live feed updates
- Restructure activity feed HTML to support live prepending
- Add slide-in animation for new activity items
- Update CORS to allow credentials for SignalR

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

TaskTracker.Api/wwwroot/js/app.js

@@ -272,4 +272,60 @@
         }
     });
 
+    // ========================================
+    // SignalR — Real-time Activity Feed
+    // ========================================
+
+    function initActivityHub() {
+        var feed = document.getElementById('activity-feed');
+        if (!feed) return; // Not on the Analytics page
+
+        var connection = new signalR.HubConnectionBuilder()
+            .withUrl('/hubs/activity')
+            .withAutomaticReconnect()
+            .build();
+
+        connection.on('NewActivity', function(data) {
+            // Remove the empty-state placeholder if present
+            var empty = document.getElementById('activity-empty');
+            if (empty) empty.remove();
+
+            var item = document.createElement('div');
+            item.className = 'activity-item activity-item--new';
+
+            var displayText = data.url || data.windowTitle || '';
+            // Escape HTML to prevent XSS
+            var div = document.createElement('div');
+            div.textContent = data.appName || '';
+            var safeApp = div.innerHTML;
+            div.textContent = displayText;
+            var safeTitle = div.innerHTML;
+
+            item.innerHTML =
+                '<span class="activity-dot" style="background: var(--color-accent)"></span>' +
+                '<div class="activity-line"></div>' +
+                '<div class="activity-info">' +
+                    '<span class="activity-app">' + safeApp + '</span>' +
+                    '<span class="activity-title">' + safeTitle + '</span>' +
+                    '<span class="activity-time">just now</span>' +
+                '</div>';
+
+            feed.insertBefore(item, feed.firstChild);
+
+            // Cap visible items at 100 to prevent memory bloat
+            var items = feed.querySelectorAll('.activity-item');
+            if (items.length > 100) {
+                items[items.length - 1].remove();
+            }
+        });
+
+        connection.start().catch(function(err) {
+            console.error('SignalR connection error:', err);
+        });
+    }
+
+    document.addEventListener('DOMContentLoaded', function() {
+        initActivityHub();
+    });
+
 })();