feat(FN-848): merge Activity and Agent Log into unified Logs tab

- Consolidate separate Activity and Agent Log tabs into a single Logs tab with toggle
- Add toggle UI to switch between activity log and agent log views
- Add CSS styles for the new toggle component and log tab layout
- Simplify TaskDetailModal tab structure by removing two tabs in favor of one

packages/dashboard/app/styles.css

@@ -4956,6 +4956,41 @@ body {
   font-weight: 600;
 }
 
+/* === Log Subview Toggle === */
+.log-subview-toggle {
+  display: inline-flex;
+  gap: 0;
+  background: var(--card);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  padding: 2px;
+  margin-bottom: var(--space-md);
+}
+
+.log-subview-btn {
+  padding: 4px 12px;
+  background: none;
+  border: none;
+  border-radius: var(--radius-sm);
+  color: var(--text-muted);
+  cursor: pointer;
+  font-size: 12px;
+  font-weight: 500;
+  font-family: inherit;
+  transition: color var(--transition-fast), background var(--transition-fast);
+}
+
+.log-subview-btn:hover {
+  color: var(--text);
+  background: var(--card-hover);
+}
+
+.log-subview-btn-active {
+  color: var(--text);
+  background: var(--surface);
+  box-shadow: var(--shadow-sm);
+}
+
 /* === Mobile Responsive Overrides ===
    On narrow viewports (≤768px) the board switches from a 5-column grid to a
    horizontally-scrollable flex layout so only one scrollbar appears.  Each