feat(frontend): Implement Task management components - Sprint 4 Story 2

Add complete Task CRUD UI for Story detail page with inline creation,
status toggling, filtering, and sorting capabilities.

Changes:
- Created TaskList component with filters, sorting, and progress bar
- Created TaskCard component with checkbox status toggle and metadata
- Created TaskQuickAdd component for inline Task creation
- Added shadcn/ui checkbox and alert components
- All components use existing Task hooks (useTasks, useCreateTask, etc.)

Components:
- components/tasks/task-list.tsx (150 lines)
- components/tasks/task-card.tsx (160 lines)
- components/tasks/task-quick-add.tsx (180 lines)
- components/ui/checkbox.tsx (shadcn/ui)
- components/ui/alert.tsx (shadcn/ui)

Features:
- Task list with real-time count and progress bar
- Filter by: All, Active, Completed
- Sort by: Recent, Alphabetical, Status
- Checkbox toggle for instant status change (optimistic UI)
- Inline Quick Add form for fast Task creation
- Priority badges and metadata display
- Loading states and error handling
- Empty state messaging

Sprint 4 Story 2: Task Management in Story Detail
Task 3: Implement TaskList, TaskCard, TaskQuickAdd components

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/ui/alert.tsx

@@ -0,0 +1,66 @@
+import * as React from "react"
+import { cva, type VariantProps } from "class-variance-authority"
+
+import { cn } from "@/lib/utils"
+
+const alertVariants = cva(
+  "relative w-full rounded-lg border px-4 py-3 text-sm grid has-[>svg]:grid-cols-[calc(var(--spacing)*4)_1fr] grid-cols-[0_1fr] has-[>svg]:gap-x-3 gap-y-0.5 items-start [&>svg]:size-4 [&>svg]:translate-y-0.5 [&>svg]:text-current",
+  {
+    variants: {
+      variant: {
+        default: "bg-card text-card-foreground",
+        destructive:
+          "text-destructive bg-card [&>svg]:text-current *:data-[slot=alert-description]:text-destructive/90",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+    },
+  }
+)
+
+function Alert({
+  className,
+  variant,
+  ...props
+}: React.ComponentProps<"div"> & VariantProps<typeof alertVariants>) {
+  return (
+    <div
+      data-slot="alert"
+      role="alert"
+      className={cn(alertVariants({ variant }), className)}
+      {...props}
+    />
+  )
+}
+
+function AlertTitle({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-title"
+      className={cn(
+        "col-start-2 line-clamp-1 min-h-4 font-medium tracking-tight",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+function AlertDescription({
+  className,
+  ...props
+}: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="alert-description"
+      className={cn(
+        "text-muted-foreground col-start-2 grid justify-items-start gap-1 text-sm [&_p]:leading-relaxed",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Alert, AlertTitle, AlertDescription }