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/board/ColumnHeader.tsx

@@ -20,6 +20,7 @@ import type { Column, ColumnWidth } from "@/types/board";
 interface ColumnHeaderProps {
   column: Column;
   cardCount: number;
+  filteredCount?: number;
 }
 
 const COLOR_PRESETS = [
@@ -35,7 +36,7 @@ const COLOR_PRESETS = [
   { hue: "0", label: "Slate" },
 ];
 
-export function ColumnHeader({ column, cardCount }: ColumnHeaderProps) {
+export function ColumnHeader({ column, cardCount, filteredCount }: ColumnHeaderProps) {
   const [editing, setEditing] = useState(false);
   const [editValue, setEditValue] = useState(column.title);
   const inputRef = useRef<HTMLInputElement>(null);
@@ -107,7 +108,7 @@ export function ColumnHeader({ column, cardCount }: ColumnHeaderProps) {
               ? "text-[oklch(65%_0.15_70)]"
               : "text-pylon-text-secondary"
         }`}>
-          {cardCount}{column.wipLimit != null ? `/${column.wipLimit}` : ""}
+          {filteredCount != null ? `${filteredCount} of ` : ""}{cardCount}{column.wipLimit != null ? `/${column.wipLimit}` : ""}
         </span>
       </div>