UI polish: notes/tasks list views

- NotesListView: skeleton shimmer for grid and list modes; grid columns change from fixed 3 to auto-fill(260px)
- NoteCard compact: flat border-bottom row style instead of stacked mini-cards; gradient fade mask on grid preview text
- TaskCard compact: flat border-bottom row style; show up to 2 tags
- TasksListView: gradient + shadow on New Task button (matches NotesListView)

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

frontend/src/components/NoteCard.vue

@@ -78,6 +78,19 @@ function goEdit() {
   align-items: center;
   gap: 0.6rem;
   padding: 0.45rem 0.75rem;
+  background: var(--color-bg-card);
+  box-shadow: none;
+  border-radius: 0;
+  border-bottom: 1px solid var(--color-border);
+  transform: none !important;
+}
+.note-card.compact:first-child {
+  border-top: 1px solid var(--color-border);
+}
+.note-card.compact:hover {
+  box-shadow: none;
+  background: rgba(99, 102, 241, 0.04);
+  transform: none;
 }
 .note-title-compact {
   font-size: 0.9rem;
@@ -137,6 +150,9 @@ function goEdit() {
   font-size: 0.9rem;
   max-height: 7.5em;
   overflow: hidden;
+  position: relative;
+  -webkit-mask-image: linear-gradient(to bottom, black 60%, transparent 100%);
+  mask-image: linear-gradient(to bottom, black 60%, transparent 100%);
 }
 .note-meta {
   display: flex;