feat(FN-1549): simplify chat creation with agent-only selection and auto title

- Remove task selection from chat creation flow
- Add agent-only chat creation with automatic title generation
- Introduce useChat hook for unified chat state management
- Update ChatView with simplified creation UI
- Add CSS styles for chat creation interface
- Add comprehensive tests for chat manager and routes
- Update routes to support agent-only chat creation

packages/dashboard/app/styles.css

@@ -27722,6 +27722,61 @@ html .column.drag-over * {
   gap: 8px;
 }
 
+/* Agent list in new chat dialog */
+.chat-new-dialog-loading,
+.chat-new-dialog-empty {
+  padding: 16px;
+  text-align: center;
+  color: var(--text-secondary);
+  font-size: 14px;
+}
+
+.chat-new-dialog-agent-list {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  max-height: 300px;
+  overflow-y: auto;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  padding: 4px;
+}
+
+.chat-new-dialog-agent-item {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 8px 12px;
+  border: none;
+  border-radius: 6px;
+  background: transparent;
+  color: var(--text);
+  font-size: 14px;
+  text-align: left;
+  cursor: pointer;
+  transition: background 0.15s;
+}
+
+.chat-new-dialog-agent-item:hover {
+  background: var(--bg-hover);
+}
+
+.chat-new-dialog-agent-item--selected {
+  background: var(--accent-color-light, rgba(59, 130, 246, 0.1));
+  border: 1px solid var(--accent-color, rgba(59, 130, 246, 0.3));
+}
+
+.chat-new-dialog-agent-name {
+  flex: 1;
+  font-weight: 500;
+}
+
+.chat-new-dialog-agent-role {
+  font-size: 12px;
+  color: var(--text-secondary);
+  text-transform: capitalize;
+}
+
 /* Ensure dropdown portal renders above dialog */
 .chat-new-dialog {
   overflow: visible;