feat: Phase 3 - filter bar, keyboard navigation, notifications, comments

- FilterBar component with text search, label chips, due date and priority dropdowns
- "/" keyboard shortcut and toolbar button to toggle filter bar
- Keyboard card navigation with J/K/H/L keys, Enter to open, Escape to clear
- Focus ring on keyboard-selected cards with auto-scroll
- Desktop notifications for due/overdue cards via tauri-plugin-notification
- CommentsSection component with add/delete and relative timestamps
- Filtered card count display in column headers

src/components/card-detail/CardDetailModal.tsx

@@ -9,6 +9,7 @@ import { LabelPicker } from "@/components/card-detail/LabelPicker";
 import { DueDatePicker } from "@/components/card-detail/DueDatePicker";
 import { AttachmentSection } from "@/components/card-detail/AttachmentSection";
 import { PriorityPicker } from "@/components/card-detail/PriorityPicker";
+import { CommentsSection } from "@/components/card-detail/CommentsSection";
 import { springs, staggerContainer, fadeSlideUp } from "@/lib/motion";
 
 interface CardDetailModalProps {
@@ -165,6 +166,15 @@ export function CardDetailModal({ cardId, onClose }: CardDetailModalProps) {
                     attachments={card.attachments}
                   />
                 </motion.div>
+
+                {/* Row 5: Comments (full width) */}
+                <motion.div
+                  className="col-span-2 rounded-lg bg-pylon-column/50 p-4"
+                  variants={fadeSlideUp}
+                  transition={springs.bouncy}
+                >
+                  <CommentsSection cardId={cardId} comments={card.comments} />
+                </motion.div>
               </motion.div>
               </OverlayScrollbarsComponent>
             </motion.div>