UI polish: hover lift, skeleton loaders, empty states, badge contrast, transitions

Card & row interactions:
- NoteCard, TaskCard, ProjectCard: translateY(-2px) lift on hover + extended transitions
- Kanban task cards (ProjectView), note rows: same lift treatment
- Task rows in flat/grouped list: soft indigo bg tint on hover
- Chat conversation items: left-border accent + bg tint on hover (was border-only)
- HomeView project mini-cards: translateY(-2px) lift on hover

Global feedback:
- Buttons: scale(0.97) on :active press (theme.css, :not(:disabled) scoped)
- TagPill: color → primary + indigo bg tint on hover
- StatusBadge: increased opacity 15% → 22% + stronger text color for readability

Loading & empty states:
- TasksListView: shimmer skeleton loader (6 rows) + rich empty state with CTA
- ProjectListView: shimmer skeleton cards (4) + rich empty state with CTA
- HomeView: section-empty messages for overdue/high-priority/notes sections
- ProjectView kanban columns: dashed-border styled empty state

Transitions & graph:
- WorkspaceView panels: panel-fade opacity transition on show/hide (v-if inner wrap)
- GraphView D3 nodes: grow to r*1.3 + bold label on mouseover (150ms transition)
- Milestone action buttons: base opacity 0 → 0.35 for discoverability

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

frontend/src/assets/theme.css

@@ -128,6 +128,13 @@ a:focus-visible {
   border-radius: var(--radius-sm);
 }
 
+button:not(:disabled):active,
+.btn:not(:disabled):active,
+[role="button"]:not(:disabled):active {
+  transform: scale(0.97);
+  transition: transform 0.08s ease;
+}
+
 /* Responsive breakpoints: 480px (phone), 768px (tablet), 1024px (desktop) */
 @media (max-width: 768px) {
   .hide-mobile {