Tasks list: smart sections view (overdue / today / this week / upcoming / no date / done)

Replaces the flat sorted list with date-aware sections that surface what
needs attention first. Completed tasks go into a collapsed section at the
bottom. Grouped-by-project mode is preserved as the second toggle option.
TaskCard compact restored to card hover/lift style.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/TaskCard.vue

@@ -122,19 +122,7 @@ function isOverdue(): boolean {
   display: flex;
   align-items: center;
   gap: 0.5rem;
-  padding: 0.4rem 0.75rem;
-  box-shadow: none;
-  border-radius: 0;
-  border-bottom: 1px solid var(--color-border);
-  transform: none !important;
-}
-.task-card.compact:first-child {
-  border-top: 1px solid var(--color-border);
-}
-.task-card.compact:hover {
-  box-shadow: none;
-  background: rgba(99, 102, 241, 0.04);
-  transform: none;
+  padding: 0.45rem 0.85rem;
 }
 
 /* Status dot */